Fontes
Estes são os fontes do programa de conexão a internet para o Debian, demais distribuiçoes usam, eu acho,formas diferentes de conexão,
no Conectiva era "adsl-start", porem o programa pode ser ampliado para outras distribuições.
No debian se usa o pacote pppoe , e os comandos são pon dsl-provider para iniciar a conexão, poff -a para finalizar e plog para o status da
conexão. O shell-script que eu criei necessita que se edite o arquivo /etc/sudoers para dar permissão sudo ao route e ao plog,
pois eles não executam como usuario normal.

Cabeçalho:

/***************************************************************************
 *   Copyright (C) 2007 by Rodolfo Ribeiro Machado   *
 *   rodolfo@Programador   *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/
#ifndef CONECTAR_H
#define CONECTAR_H

#include <ui_fConectar.h>
class util;
/**
	@author Rodolfo Ribeiro Machado <rodolfo@Programador>
*/
class fConectar_Internet : public QMainWindow,private Ui::fConectar
{
  Q_OBJECT
  public:
    fConectar_Internet(QWidget *parent = 0, const char *name = 0);

    ~fConectar_Internet();

  protected:
    class util* ut;

  private:  
    QString* retorno;

  private slots:
    void fecha_Aplicacao();
    void conecta_Internet();
    void desconecta_Internet();
    void estado_da_Conexao();
};

#endif

corpo:

/***************************************************************************
 *   Copyright (C) 2007 by Rodolfo Ribeiro Machado   *
 *   rodolfo@Programador   *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/
#include "conectar.h"
#include "util.h"
#include <QProcess>
#include <QMessageBox>
#include <QtDebug>

fConectar_Internet::fConectar_Internet(QWidget *parent, const char *name)
 : QMainWindow(parent)
{
  setupUi(this);

  this->setAttribute(Qt::WA_DeleteOnClose,true);
  
  ut=new util();

  ut->fixa_Tamanho(this);
  ut->centraliza_na_Tela(this);

  connect(botao_Sair,SIGNAL(clicked()),this,SLOT(fecha_Aplicacao()));
  connect(botao_Conectar,SIGNAL(clicked()),this,SLOT(conecta_Internet()));
  connect(botao_Desconectar,SIGNAL(clicked()),this,SLOT(desconecta_Internet()));
  connect(botao_Estado,SIGNAL(clicked()),this,SLOT(estado_da_Conexao()));
  
  retorno=new QString;
  
  *retorno=ut->lanca_Aplicativo("/Scripts/verifica_Conexao","",this);
  if (retorno->at(0)==QChar('s'))
  {
    botao_Conectar->setEnabled(false);
    QMessageBox::information(0,"Conectar à Internet","Sistema já esta conectado");  
  }
}


fConectar_Internet::~fConectar_Internet()
{
  delete retorno;
  delete ut;
}

void fConectar_Internet::fecha_Aplicacao()
{
  this->close();
}

void fConectar_Internet::conecta_Internet()
{
  *retorno=ut->lanca_Aplicativo("/Scripts/net","",this);
  QMessageBox::information(0,"Conectar à Internet",*retorno);
  *retorno=ut->lanca_Aplicativo("/Scripts/verifica_Conexao","",this);
  if (retorno->at(0)==QChar('n'))
  {
    if (!botao_Conectar->isEnabled())
      botao_Conectar->setEnabled(true);
  }
  else
    botao_Conectar->setEnabled(false);  
}

void fConectar_Internet::desconecta_Internet()
{
  *retorno=ut->lanca_Aplicativo("/Scripts/net_off","",this);
  QMessageBox::information(0,"Conectar à Internet",*retorno);
  *retorno=ut->lanca_Aplicativo("/Scripts/verifica_Conexao","",this);
  if (retorno->at(0)==QChar('n'))
  {
    if (!botao_Conectar->isEnabled())
      botao_Conectar->setEnabled(true);
  }
  

}

void fConectar_Internet::estado_da_Conexao()
{
  *retorno=ut->lanca_Aplicativo("/Scripts/estado_da_Conexao","",this);
  QMessageBox::information(0,"Conectar à Internet",*retorno);
}

main:

/***************************************************************************
 *   Copyright (C) 2007 by Rodolfo Ribeiro Machado   *
 *   rodolfo@Programador   *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/


#include <QApplication>
#include "conectar.h"

int main( int argc, char ** argv ) {
    QApplication a( argc, argv );
    fConectar_Internet * fConexao_net = new fConectar_Internet();
     
    fConexao_net->show();
    a.connect( &a, SIGNAL(lastWindowClosed()), &a, SLOT(quit()) );
    return a.exec();
}

util.h:

#ifndef UTIL_H
#define UTIL_H

class QMainWindow;
class QKeyEvent;
class QSqlQuery;
class QSqlQueryModel;
class QString;
class QTableView;
class QWidget;
class QAction;
class QDesktopWidget;
class QRect;
class QStringList;
class QLineEdit;
class QLabel;
class QCloseEvent;

/**
@author Rodolfo Ribeiro Machado,,,
*/
class util
{
  public:
    util();
    ~util();
    
    void fixa_Tamanho(QWidget* comp);
    void centraliza_na_Tela(QWidget* comp);
    QString lanca_Aplicativo(QString aplicativo,QString argumento,QWidget* comp);


};

#endif

util.cpp:

#include "util.h"

#include <QMainWindow>
#include <QDesktopWidget>
#include <QProcess>
#include <QByteArray>
#include <QVariant>
#include <QCloseEvent>


util::util()
{
}


util::~util()
{
}


void util::fixa_Tamanho(QWidget* comp)
{
  QSize* tamanho=new QSize();
  *tamanho=comp->size();
  comp->setFixedSize (*tamanho);
  delete tamanho;
}

void util::centraliza_na_Tela(QWidget* comp)
{
  QSize* tamanho=new QSize();
  *tamanho=comp->size();
  QDesktopWidget* desk=new QDesktopWidget();
  QRect rect=desk->screenGeometry(0);
    
  int * x1=new int;
  int * y1=new int;
  int * x2=new int; 
  int * y2=new int;
  rect.getCoords(x1,y1,x2,y2);
    
  comp->setGeometry((*x2-tamanho-> width ())/2,(*y2-tamanho-> height ())/2,tamanho-> width (),tamanho-> height ());
  delete tamanho;
  delete x1;
  delete x2;
  delete y1;
  delete y2;
  delete desk;
}

QString util::lanca_Aplicativo(QString aplicativo,QString argumento,QWidget* comp)
{
  QStringList argumento_2;
  argumento_2<<argumento;
  QProcess *myProcess = new QProcess(comp);

  myProcess->start(aplicativo, argumento_2);
  myProcess->waitForFinished();
 
  return myProcess->readAllStandardOutput();
  
}

Este é o arquivo gerado pelo QTDesigner, copie e salve como fConectar.ui, ao abrir no Designer ele ira reclamar a falta do arquivo de icones, substitua por um seu.


<ui version="4.0" >
 <class>fConectar</class>
 <widget class="QMainWindow" name="fConectar" >
  <property name="geometry" >
   <rect>
    <x>0</x>
    <y>0</y>
    <width>322</width>
    <height>135</height>
   </rect>
  </property>
  <property name="windowTitle" >
   <string>Conectar-se à Internet</string>
  </property>
  <property name="windowIcon" >
   <iconset resource="icones.qrc" >:/new/prefix1/icones/connect_creating.png</iconset>
  </property>
  <property name="dockNestingEnabled" >
   <bool>false</bool>
  </property>
  <widget class="QWidget" name="centralwidget" >
   <widget class="QPushButton" name="botao_Conectar" >
    <property name="geometry" >
     <rect>
      <x>6</x>
      <y>12</y>
      <width>151</width>
      <height>41</height>
     </rect>
    </property>
    <property name="text" >
     <string>&amp;Conectar</string>
    </property>
    <property name="icon" >
     <iconset resource="icones.qrc" >:/new/prefix1/icones/connect_creating.png</iconset>
    </property>
   </widget>
   <widget class="QPushButton" name="botao_Desconectar" >
    <property name="geometry" >
     <rect>
      <x>6</x>
      <y>72</y>
      <width>151</width>
      <height>41</height>
     </rect>
    </property>
    <property name="text" >
     <string>&amp;Desconectar</string>
    </property>
    <property name="icon" >
     <iconset resource="icones.qrc" >:/new/prefix1/icones/connect_no.png</iconset>
    </property>
   </widget>
   <widget class="QPushButton" name="botao_Sair" >
    <property name="geometry" >
     <rect>
      <x>166</x>
      <y>72</y>
      <width>151</width>
      <height>41</height>
     </rect>
    </property>
    <property name="text" >
     <string>&amp;Sair</string>
    </property>
    <property name="icon" >
     <iconset resource="icones.qrc" >:/new/prefix1/icones/exit.png</iconset>
    </property>
   </widget>
   <widget class="QPushButton" name="botao_Estado" >
    <property name="geometry" >
     <rect>
      <x>166</x>
      <y>12</y>
      <width>151</width>
      <height>41</height>
     </rect>
    </property>
    <property name="text" >
     <string>&amp;Estado da Conexão</string>
    </property>
    <property name="icon" >
     <iconset resource="icones.qrc" >:/new/prefix1/icones/connect_established.png</iconset>
    </property>
   </widget>
  </widget>
  <widget class="QStatusBar" name="statusbar" />
 </widget>
 <tabstops>
  <tabstop>botao_Conectar</tabstop>
  <tabstop>botao_Estado</tabstop>
  <tabstop>botao_Desconectar</tabstop>
  <tabstop>botao_Sair</tabstop>
 </tabstops>
 <resources>
  <include location="icones.qrc" />
 </resources>
 <connections/>
</ui>


Agora são os shell-scripts:

nomeie este como "verifica_Conexao"

#!/bin/bash
if ps -el | grep ppp > /dev/null; then
  echo s;
else
  echo n
fi;

nomeie este como "net"

#!/bin/bash
if [ -e /usr/bin/pon ]; then 
  if pon dsl-provider; then
    sleep 3;
    if /sbin/ifconfig | grep ppp0; then
      if sudo /sbin/route add default ppp0; then
        echo Conexão bem sucedida.;
      else
        /usr/bin/poff -a;
        sleep 5;
        echo Não foi possivel estabelecer uma conexão;
      fi;
    else
      /usr/bin/poff -a; 
      echo Não foi possivel estabelecer uma conexão; 
    fi;
  else
    echo Não foi possivel estabelecer uma conexão;
  fi;
else
  echo /usr/bin/pon não esta instalado!;
fi;

nomeie este como "net_off"

#!/bin/bash
if /usr/bin/poff -a; then
  sleep 5;
  echo Conexão terminada;
fi;

nomeie este como "estado_da_Conexao"

#!/bin/bash
sudo plog 

Crie um arquivo texto com os nomes indicados para cada um e salve em um diretório de sua preferencia, tomando o cuidado de alterar os fontes 
para o caminho de seu diretório.
Substituam todos os caminhos de diretórios no fonte pelos seus.