I'd go for the 6600GT over the 9800 Pro. The price difference for an 8x AGP model is barely a factor.
edit:
sorry misread your post. Thought you were going to upgrade from the 9600XT to the 9800Pro.
The 9600XT only has 4 pipes, the 9800Pro has 8 pipes. The clocks are also lower for the 9600XT. You should definately be able to play the game though, depending on your CPU/RAM config.
IF you do decide to upgrade, go for a 6600GT. If your budget permits, go for a 6800U.
[This message has been edited by F34R (edited 09-10-2005 @ 10:52 PM).]