FIRST OF ALL, you must be in speed mode and have the nvidia driver ready with direct rendering (test with : "#glxinfo |grep direct"). You have to uninstall all packages "compiz" with synaptic, otherwise you'll have a conflict with beryl.

Add this repersitory in synaptic (more information on beryl-repersitory ) :
deb http://ubuntu.beryl-project.org feisty main

Add the authentification package :
#wget http://ubuntu.beryl-project.org/root@lupine.me.uk.gpg -O- | sudo apt-key add -

After the update of your synaptic, use the keyword "beryl" and install everything except packages like xxx-dev or xxx-dbg. AND install emerald themes package (except xxx-dev and xxx-dbg).

Finally, start beryl in console or in your gnome menu "system". Don't worry, the first time the windows will appear without borders, choose an Emerald theme in the beryl menu and it will work...
ENJOY !!!