To make KDE the dominant Desktop Environment instead of GNOME
edit /etc/inittab
at the bottom you’ll find a line that reads x:5:respawn and so on
it’ll probably point at prefdm
make it point at /usr/bin/kdm instead
Another solution:
Edit /etc/sysconfig/desktop to contain
DESKTOP=KDE
DISPLAYMANAGER=KDE
This will make KDE the default desktop and kdm the default login manager.