HOW-TO: ATI fglrx driver 8.16.20

sudo apt-get remove xorg-driver-fglrx
sudo apt-get remove linux-restricted-modules-$(uname -r)
sudo dpkg-reconfigure xserver-xorg #Select the ATI driver

reboot

sudo apt-get install xorg-driver-fglrx
sudo apt-get install linux-restricted-modules-$(uname -r) #Okay if it is already installed
sudo dpkg-reconfigure xserver-xorg #Select the fglrx driver

http://ubuntuforums.org/showthread.php?p=408111