Please tell us what card you have at the moment? It all depends on if you are a big gamer or just playing games for fun. If you are just doing it for fun and have a low budget i would advise you to go for the 8600 GT(or GTS) series. I had a Foxconn 8600 GT and it performed great. Really miss that card. Or the 8500 GT - not the best card for gaming, but cheap. If you are seriously into gaming like I am, then I would go for the 8800GT...GREAT CARD!! ( need a much bigger budget)
I currently have the Inno 3D 9800GT OC 512MB Gddr3. It runs Call of Duty 4 like a dream. Fullblast, everything on its highest. It also runs Gears of War on Dx 10 without a problem. And it only cost me R1900.00. Great deal!! (almost half the price of a 8800GT, and my card kicks its butt!)
How did you get your 9800GT to work on your ASUS P5N-D MB? I got a black screen after the progress bar on Vista64. I don't know why, but it boots fine without the driver installed. What SBIOS is on your MB?