I was just wondering if in order to run 2 cards in Crossfire/SLI mode, do they have to be the same card? I know ATI - Crossfire and Nvidia - SLI but would I have to use the same ATI cards? Can I use two different ATI cards? What are the limitations on those cards?

For Ati the have to be the same core. They can be different manufacturers, memory sizes or clocked differently (each card runs at it own speed)

For example:

HD3870 + HD3850
HD4870 + HD4850

http://game.amd.com/us-en/content/image ... July08.jpg

For Nvidia they can be different manufacturers, different clocks(card clocked to lower speed) and different memory size. I suspect that the number of shaders must be matched as well, which screws up things on a pretty collosal scale on the Nivida side as they have cards with the same names that are different, and cards with different names that are the same (9800GT = 8800GT)