xfce Session and KDM

[Robert Tilley]

My main GUI is KDE 3.1 running kdm.  How can I add an xfce session to my list 
of window managers?

The session "xfwm4" exists in the list after apt-get installing xfce4.  
However, after choosing it from kdm and logging in -- a blank screen is all 
that appears.  No left, middle, or right mouse clicks cause any reaction and 
I am forced to do a three-finger salute (ctrl-alt-backspace) to go back to 
KDE.

I would like to experiment with xfce4 and need help.
-- 
Comments are appreciated,

Bob