Howto install Beryl with Nvidia on Ubuntu Feisty Fawn
Some nice guide for installing beryl: http://www.ubuntugeek.com/how-to-install-beryl-with-latest-nvidia-drivers-in-ubuntu-feisty-fawn.html
Just one note: instead of executing
sudo apt-get install beryl emerald-themes
Try to exec
sudo apt-get install beryl beryl-manager emerald-themes