Try:
Code:
rm -rf ~/.kde/Autostart/*
If this doesn't work all I can say is manually close all the apps, perhaps you will need to ps aux and kill the processes...then log out of kde.
Hmm, did a bit more research, and it would seem that the session data is actually in:
Code:
~/.kde/share/config/session/
So remove the contents of this directory before you startx...