Re: Video card question
Keep in mind a projector that can handle that type of resolution you're looking at is going to be EXPENSIVE. Like on the order of several thousands of dollars.
I have a DLP projector at home that does something like 800x488 or something and it looks fine for things like movies and old games.
If you buy a 720p projector, that will be plenty, but you'll use little of that graphics horsepower.
Three GPUs (or any SLI/CrossFire arrangement) is best left for a high resolution single monitor in a high end game with all of the eye candy & antialiasing/ansiotropic filtering turned on. If you don't use AA/Aniso & the highest resolution you can of a monitor 24" or higher, then you're wasting your power and your time. SLI/CF is useless below 1650x1080 on the newest cards. I had two 8800 GTS's in SLI and even at 1650x1080 they weren't stressed at all.