Welcome to TPU! yea your 9800GT will be fine. for 100$ you really can get a new card that would be better unless you buy a used one from here in the forums and that really wouldnt be too big of a diffrence. If you a gamer and want a good card either wait til the new Nvidias come out or get a 5870 when you can afford it.
7970 3GB *Unlocked* = 8 Threads
5770 1GB OCed = 2 Threads