Where are my wms?

[Robert Tilley <tilleyrw@cfl.rr.com>]

debian-rtg:/home/tilleyrw# update-alternatives --config x-session-manager

There is only 1 program which provides x-session-manager
(/usr/bin/startkde). Nothing to configure.

Why does Linux think that KDE is the only window manager on my system?  I just 
perform a dpkg -l to verify that at least blackbox and xfce are installed.

ii  blackbox       0.65.0-1.2     Window manager for X
ii  xfce4          4.0.0.final-1  Installs XFce4 core and scripts to set it up

As you can tell from the listings, I'm running unstable.  But back to the 
reason for this posting.  I want to easily switch wm's between KDE/BB/XFCE.

Any suggestions?
-- 
Comments are appreciated,

Bob