Here you go from:
http://www.plig.org/xwinman/basics.html
If running X from the command line, using "startx": Create a file in your home directory called
Code:
/home/user/.xinitrc
Edit and add the following to that file:
Replace
windowmanager with one of these options:
KDE (kdm) = startkde
Gnome (gdm) = gnome-session
Blackbox = blackbox
FVWM = fvwm
Window Maker = wmaker
IceWM = icewm
If using xdm create a file called .xsession instead and add the above info.
Also, if these files already exist, make a backup before you edit them.
P.S. You could also just run kdm (or gdm) as root. Then when you log out run "killall kdm"