this is a "highly technical" forum, there is tech support, video, and general hardware for these types of questions. there *was* a stickied post mentioning this but its gone at the moment...how people keep mistaking *highly technical* for *tech support* is beyond me, perhaps you're all in a hurry
anyway, itll work, but obviously only at the 2x speed. there are, by the way, also FAQ's at anandtech that would answer that. all agp ports/cards are fully compatible (forward and backwards)
next time use the appropriate forum or search FAQ's