How can you tell if the board supports Crossfire or SLI? I imagine it's specific to the chipset?
It actually says on that page for the Foxconn one that it supports Crossfire ("Perfect Intel P45 next gen crossfire solution & more") its located right on the top, below the product title.
But its usually like this P35, P45, X38, X48 may or may not support Crossfire (depends if it comes with more than one PCI-Express slot) (Intel chipset).
680i, 780i, 790i, 750i will support SLI (these are all Nvidia chipset), some
of the boards will say on their title that it supports SLI.