Kopete is KDE default instant messaging client. In newer versions, there is an option to launch the application when you log into KDE. If you have an older version, this functionality is not directly configurable from Kopete. You can achieve the same result by copying Kopete's desktop file into your KDE Autostart folder. Open a console (konsole, xterm, etc) and execute this command:
cp /usr/share/applications/kde/kopete.desktop ~/.kde/Autostart/
The next time you log-in, Kopete will get launched automatically.
