Personally I use Gentoo when I'm not gaming on my XP(
)
As long as your kernel is correctly configured... installing ati drivers should not be a problem, and there is a good ATI HOW-TO on gentoo-wiki.
To install the drivers you just need to login as root, and type
and you're done.. It's configured, compiled and installed, with all the necessary patches (if you have a VIA and you need AGP support, for example)
But.. like the previous guy said, you should choose a distribution that fits your needs