Any motherboard that supports regular PCI Express will be able to run that card, but it will be limited to the 16x bandwidth of PCI-e. It's like running an 8x AGP card in a 4x AGP slot: it'll work; the card will just be limited to 4x.
With the 8800GT, there should be little, if any, performance difference between running it in a PCI-e and PCI-e 2.0 slot. To my knowledge, the 8800GT doesn't exceed the 16x bandwidth of PCI-e.