There are at least two methods that can be used to install the fglrx driver in Debian. The first, and recommended way is to use the native Debian packages directly from the non-free repository.
Get the packages updates:
sudo aptitude update
Install your kernel headers:
sudo aptitude install linux-headers-`uname -r`
Download and install the necessary compilers:
sudo aptitude install build-essential
Get the packages updates:
sudo aptitude update
Install the driver:
sudo aptitude install module-assistant fglrx-driver fglrx-kernel-src
Build and install the module:
sudo module-assistant auto-install fglrx-kernel-src
After this you will need:
sudo aticonfig --initial
This will update your xorg.conf to use the new driver. Restart for the changes to take effect.
tymonn 