To add to the above responses- in addition to having to use two cards running the same driver, you will also almost certainly have to use the Vista basic desktop theme. Aero effects will work with multiple (non-SLI/CF) video cards, but there is a heavy performance penalty, even in 2D. For example, the monitor(s) running on the non-primary card(s) will demonstrate choppy scrolling on webpages, office applications, etc. There is still a slight performance penalty with Aero turned off, but it is manageable. In XP, this penalty could be corrected by turning 2D acceleration off- this option is not currently available in Vista.