Is it possible to install any video card in my imac? I'm thinking of installing a High Def one or something better than i have (GeForce 8800 Ultra would be nice). I know the computer is really thin and small so there must be some size restrictions on the card and the OS might not like it. I have a 20' Intel Core 2 Duo with an ATI Raedon X1600 128mb So far ive searched around forums and have only found muppets who ask if they can upgrade their integrated GMA like they dont know it's stuck to thier motherboard. Has anyone tried this before?