MSI is showcasing a 975 motherboard that runs two Crossfire cards. As of this show MSI even gives technical support for 975 boards running the two ATI cards.

All you need to do is to plug the two cards and install them. Otherwise it should run. An ATI marchitecture chap told us that you could run two Crossfire cards on an SLI motherboard. It is all to do with software. Some Nvidia elements confirmed the claim that Crossfire could run at SLI and vice versa.