The demo did not support the GF4 and the offical stance last I knew was they weren't going to support it. The word is NVIDIA had some influence on that decision to make gamers upgrade their cards, but who knows *shrug*. There is a hack out there somewhere that allowed the GF4 to work, but it didn't sound that reliable.
As for EB and getting a hold of the game, it'll probably depend alot on your local EB. Mine will be waiting for me when I get home, according to FedEx online :). I went with the ebworld pre-order.. free overnight shipping and a free headset. Don't hate me because I'm playing BF2 tonight.