The GTX 260 is probably the best GPU you could get on the market if you're on a cheap budget. I do recommend you have a moderate sized case for room purposes. This card is pretty "huge". Also make sure you have a good PSU. If you have a lot of power consuming parts I'm pretty sure you'll need something around 750W. With a 9800 GTX you'd get occasional blackouts even with a 650 W PSU.
Also continuing about the cards.. If you want to use less power, have more room in your case, and to save about 30-40 dollars. Then you should get a 9800 GTX. It only performs a little worse than the GTX 260, but for those three it might be worth it.
As for the FPS. Shadow is right about HDR, AA, and Anisotropic. You don't really need them. Also, if you're not really competitive regarding Reg CS then you can make the Shadow Details as Low. FPS booster. You should also check out Kaizen's CS: Source FPS Config. I quote - "While I developed my config primarily for performance, I tried to minimize losses of visual quality and I believe I achieved a happy medium." It's a great config.
P.S: You don't really need to download anything to see your PC specs. Just run dxdiag on the command prompt or "run" feature. It doesn't show a couple things though.