I am running a gateway Gateway GT5676 with Vista Home Premium x64 and I added a Diamond hd3450 graphics card to the system to boost the capability without spending big bucks. ATI did no one a favor when they didn't release a how- to with crossfire-x; it took quite a bit of fiddling and forum searching to get it working but in the end I got the win exp rating up to 4.0 and quite a boost in game performance.
At any rate I'd like to pass on that you need to take video out from the integrated onboard vga plug and when crossfire-x is enabled the vid out on the discret card is disabled by catalyst control center when crosfir is enabled but the card still runs in support of the onboard grapghics and does increase frames and win exp measurably.

JEF

PS: lowly Gateway GT5676 , Diamond HD3450, Vista hp x-64