According to information gathered, some early information about the CrossFire is that it will only be available on X850 and X800 series first. Current cards can only be used as secondary (slave) cards and the primary card will only be available from ATi. The slave will connect to the master card through DVI like connector through an external cable. The primary card will currently work with x800 or x850 as secondary and it will not be able to pair up with integrated graphics as yet (no such chipset yet).

The cards can only be used on ATi RD400 or RD480 mainboards. This solution is more flexible than the NV SLI technique.

Source:OCWorkbench