Compatible? Yes. Ideal? That's the question.
A PCIe 3.0 x16 video card will work in a PCIe 2.0 x1 slot. It will just be slow. Compatibility is rarely a problem. Since you have an x16 slot, the card and motherboard are not bottlenecked by that. I have to look at the specs to see if that x16 slot is PCIe 3.0 or PCIe 2.0, but even if they are 2.0 lanes you should get good performance.
EDIT: LGA775? That's a bit of an antique. What CPU are your running in it? Someone who knows more about modern graphics than I do might say that the card is overkill for the board / cpu combination.
EDIT2: They are PCIe 2.3 lanes. Reasonable bandwidth. Try it.