Prepare your system
First you need to install the following packages
#apt-get install module-assistant fglrx-driver fglrx-kernel-src
Build and install module
module-assistant auto-install fglrx-kernel-src
Update xorg.conf file
Use the following command to Update xorg.conf file
after completing configuration you need to restart your system.
You can test to see if the restricted driver using the following command
Output looks similar to the below
display: :0.0 screen: 0
OpenGL vendor string: ATI Technologies Inc.
OpenGL renderer string: ATI Radeon X1200 Series
OpenGL version string: 2.1.8304 Release
Note:- If you get an update of the kernel from say linux-image-2.6.26-2-686 to linux-image-2.6.26-3-686 it may bork the drivers, which would need uninstalling the drivers and recompiling of the drivers.