There is a folder under your home dir called .kde ( . for hidden) there's a dir called autostart where you can put all the things you want ran when you log in KDE.
However, note that this will only work with KDE and the specific user that has that script in his personal KDE profile dir. By what you wrote I assume that's what you wanted to do.
Running:
Pentium D 3GHz Dual Core - 2GB - Ubuntu 9.04
PIII 850MHz - 256MB - Ubuntu 8.04 Server
Registered Linux user number 312827