You didn't say whether your old card was PCI, or AGP. We know for certain it is NOT PCI-express

My ATI 9800 Pro card could still run the game, but I have gone to an ATI 850x Both are AGP cards, but I think the 859 would have trouble with your power supply. The 9800 card is a strong card even for an old one.
On the other hand, that computer is an old timer, and any upgrading would be throwing good money after bad and a waste in my opinion. I just paid $300 for a computer for the wife. Its nothing special, but with my 9800 in it it will play the game with no problem. Save up some cash, and get yourself a new computer.