I've never had a dual-GPU mobo before, so I don't know -- can an ATI crossfire-ready card work in a system just by itself? They have good deals on the x1900GTs on newegg now, and they all say Crossfire.
I know there's about a 99.99999% it will work by itself, but I'd be mad to be that .00001% chance.
I know there's about a 99.99999% it will work by itself, but I'd be mad to be that .00001% chance.