To enable the menu in CentOS 6.2 and SL 6.2 you'll need to install both compiz-gnome and desktop-effects packages assuming 3D drivers are installed.
compiz-gnome provides the compiz window manager and integration with the GNOME desktop environment while desktop-effects had a simple but useful menu to turn on/off the compiz effects.
# yum install desktop-effects compiz-gnome
Now simply point to System -> Preferences -> Desktop Effects and enable the Compiz option. I personally like to also enable the Windows Wobble when Moved option ;)