F16: window manager for xfce has disappeared

[sean darcy]

Running XFCE. yum upgrade'd yesterday, now there's no window manager. 
Stuck using gnome.

What is the xfce wm? And where is it turned on?

BTW:

switchdesk kde
Red Hat Linux switchdesk 4.0
Copyright (C) 1999-2010 Red Hat, Inc
Redistributable under the terms of the GNU General Public License
ERROR: KDE is not installed on your machine! to install KDE, please type
yum groupinstall "KDE (K Desktop Environment)"

yum groupinstall "KDE (K Desktop Environment)"
Loaded plugins: langpacks, presto, refresh-packagekit
Setting up Group Process
Warning: Group KDE (K Desktop Environment) does not exist.
No packages in any requested group available to install or update

and yum groupinstall kde fails with broken deps!

sean