Welcome to the world of AMD and getting more for your money.
You built a F53? Any good NVDA 400 speed DDR card will work just fine in it. There is a very good deal on the Geforce 5600 with 256MB of DDR 400 RAM onboard at Tigerdirect.com. About $120 after rebate.
I'm dying to see the PCPitstop test results on your new machine.
BT
EDIT
MSFT has a free beta version of 64 bit Win XP available for download.