Well, you could create a: .xinitrc file in your home directory and specify a wm you want to use like this:
exec /usr/bin/<wmnamehere>
without the <>
And then you should logout to the console and the net time you type startx it will load the new Window Manager. If you don't like other wm's you can always delete the .xinitrc and load your default KDE. Good Luc!