Intel chipset = Crossfire Nvidia chipset = SLI if your gonna run Crossfire, you really wanna have 2 pci-e x16 2.0 slots, so get an X38 or X48 chipset (there isnt really any difference between them, so get X38 cos its probbly cheaper) X48 does support DDR2, DDR2 is probbly the best to get since its cheaper then DDR3 and not that much slower. The difference between X48 and P45 is that X48 can run 2 Ati-cards at pci-e x16 speed, where the P45 chipset will change back to 2x pci-e x8 when you run 2 Ati cards, when you use only 1 card they will both run it at x16.