It would make a whole heckuva lot of sense to first upgrade your system from Sarge to the current Stable release, Etch. Read the
Release notes. Once that's done, you'll be able to install fglrx, version 8.28.8, from the Debian repositories. It supports your card.
Trying to install the current drivers from ATI will only bring you grief.
Edit: Cheez! A 2 year old thread resurrected by a newbie. Why didn't I notice that first.