Don't quote me on this but I think Linux support for nVidia is better than ATI.

Buying hardware is always tricky, the balancing act between performance and affordability. Before I got into gaming in a big way I would never consider paying more than £50 on a graphics card. Since however I'm looking around to replace my year old nVidia 7900 GT. It cost around £300 and I would be looking to spend that again. I have to upgrade my CPU next and as that means new MoBo and RAM the G/Card will have to wait. Grrrrr...

My advise would be to go for an old top of the line card rather than one that is made from day one, to be budget. So maybe something from BFG rather than "No Name" generic. Old stock that has been discounted rather than a budget card.

If gaming is your thing then try to keep you OS as light as possible. Your into Linux so you have more options or at least more power over what is running. Maybe set up a different account on login one that you can trim down to the bare minimum for what you need to get the job done, namely gaming.

Personally I have two PC's. Linux for normal PC stuff, internet, office, movies and music. Windows XP just for gaming, that's it! If it's not needed for running a game or keeping it stable then it's not installed...

Good luck with your buying it's the most complicated and heart wrenching part of computing. Most of us here are not novices, we know how to configure them, how to keep them running right, how to build them and stuff. Get the buying it wrong, and you will be kicking yourself for months if not years...