Yeah you'll be fine Chazzman. As Mact stated, just because it's a Crossfire motherboard, you don't have to have two video cards in there! That just means it has the ABILITY to do so. : )
Also, the only issue in regards to compatibility for video cards and slots is if you try to put a PCI-E 2.1 card in a PCI-E 1.0 slot. But this isn't the case for you I think.