It's easier to setup a nVidia based card under Linux. I had GF 4200 and it was no problem. Suse
even offers an automated download/install of the drivers (it works). However, if you want a 9800
it's possible, but the installation is a pain in the a$$ if you never did it before. There are numerous threads on LQ regarding the installation on different mobos under Suse 9.0. I have my sapphire 9800 pro running and play UT and UT-2003 and it's no prob (but it did run with the 4200 either).
If I were you, i would stay with the 4600 a little longer because it's still a fast card. Lean back and wait for the prices to come down, especially considering, that one can't take advantage of Directx 9(or whatever version) under linux