Well you certainly can't use an integrated headset on that frame, the headtubes are different y'see. As far as I'm concerned, as long as the bearing on the fork fits in the cup on the frame it'll be fine (compare the bearing with the original from that headset if you still have it, most likely the standard size though, unless it's a sealed headset), but you might have issues with keeping dirt and stuff out, and it might look a bit odd. Other than that, it's new fork or new frame time I'm affraid.