I am trying to figure out what to get i have aobut 300 dollars i really could move it up to 450 dollars if i want but i really need a card that will fly on the new game that is coming out called tribes 2 since i think that my current card will die on the great new graphics. Im also going to be picking up a 800mhz pentium . So if you could please tell me which Geforce is the best of which Radeon is the best for about 300 dollars i would appreciate it.

i have a

550 mhz pentium 3
128mb of ram
Abit be6-II
WD 15 gig 7200 rpm
PCI 512 sound card
Diamond stealth III extreme s540 (long name kinda crappy card)
all in wonderful Addtronics case (worth the cash)