Well, I dont know how much different the 9800 Pro is from the XT but I do know for a fact it will fit the Pro. I had a 9800 Pro from visiontek.
If you do end up getting it, make sure to install the neoprene gasket on the backside of the card. Also go to an automotive store and pick up a pakcet of di electric grease if you already havent done so.
On the 9800 pro I ran it up to 485mhz......then my water cooling system failed and it killed the card and cooler both. Nice smell!