Pretty simple. I crossfired 5850s just last week. Basically just plug them into the proper adjacent PCIe slots and plug in the power cables from the PSU. Then, they come with a Crossfire connector ribbon, so you attach that (it's near the "front" where the output bracket is). You only need 1 connector per 2 cards, the reason they have a 2nd connection spot is for tri and quadfire. Anyway, once that is done just boot up and in ATI Catalyst Control Center, there will be a new option in the dropdown menu for Crossfire. Go to there, check the "Enable Crossfire" box, hit apply. Done.