On Ubuntu Documentation you can find the CompositeManager/Xgl Howto for Ubuntu.
There is also an howto on the official Beryl Homepage: Install Beryl on Ubuntu Feisty with XGL – Beryl Wiki
Complete How To: Dell Inspiron 6400 also covers the setup of Beryl on Ubuntu.
If you want to use Beryl instead of Compiz you need to extract beryl-xgl from http://ubuntu.beryl-project.org/pool/feisty/main/0.2.0/beryl-core_0.2.0~0beryl1_i386.deb and copy to /usr/bin. You can refer to this bug for more details.