Here are some good links that may help you.
I fell into similar trouble when trying to use debian with my geforce 4 mx 440.
These links are from gentoo, but maybe you can apt-get the same packages in Debian.
- this one is for an nforce2 board and is for Debian.
if you read the gentoo links, it mentions xfree-drm, among other things. The ati driver is said to be better for 3d, compared to xfree-drm.
So I would give the third link a try, to get the ati-drivers to work.
It also mentions having trouble installing ati-drivers after aliening it to deb, but tells you how to fix that problem.
Hope this helps. If all else fails use Gentoo, and the gaming kernel.
"This is all hot air however, for I have no experience in any of these topics"