[CentOS] Changing Window Mangager in X

Hi.  I've been running CentOS 4 since it was first released.  I just 
updated (via yum) to 4.3 yesterday (with no problems as most would 
guess!).  My system runs X on start up (initlevel 5) and uses gdm as the 
display manager.  I know that when I first installed CentOS 4 with GNOME 
as the default desktop, it came with metacity as the window manager (in 
fact it is still installed and I've never touched any of the X 
settings).  I would like to try another window manager (I saw one in the 
CentOS extras repository).  Can someone sort of guide me as to what I 
need to do to "run" a different window manager in X?  The window manager 
that I want to try is 'xfwm4'. Thanks.

Sincerely
Jose