Hi, a bit confused here. I thought I read ATI doesn't support Linux that well. Nvidia does, albeit closed source. I use Nvidia which works fine (thanks to the hints in this list).
The way I understand it is that nvidia has better closed-source drivers for linux, but jealously guards their hardware, making an open source driver basically impossible.
ATI, on the other hand, releases crappy closed-source drivers, but releases hardware specs for their older models, making open-source drivers possible.
Suffice it to say, I have a radeon 9000, and whatever driver Fedora automatically detected and chose to use for my card works great in tuxracer, I didn't have to install anything extra after the base install to get good 3d working.