Can I buy the 8800 GT card for the Mac Pro if I choose to purchase the default configuration today? My work lets me get a discount at the local Apple Store, but they only carry the lowest end Mac Pro (2700 ish) and the highest (4700 ish) . Since the upper is out of my price range and the only real upgrade that I would need soon is the video card, I just need to know if it can be purchased separately from Apple or from a 3rd party.