Weird Things Afoot in Assassin’s Creed

I finally received my replacement video card for my recently deceased 7950GT .. eVGA sent me an 8800GT! It’s more awesome then I’ve even heard from other people, in short I love this card but here’s what’s going on. Assassin’s Creed is playing in a window on my new 8800GT even though the game itself has no controls for playing in a window or fullscreen and should always run fullscreen. I have no idea how to fix this slight problem so any help would be appreciated. Thanks.