I Currently use two monitors on Windows XP, with a Geforce 6800GT dual-DVI card. The nvidia drivers will only allow two display devices (two monitors or a monitor plus TV) per card, so to run more than two screens, you need two or more cards - or a specialist card. As far as I am aware you can run as many screens as you have graphics cards to drive them, so with two graphics cards you could easily drive four screens, and so on.