How about Panorama Maker (
http://www.arcsoft.com/products/panoramamaker/)? I haven't used it, but it looks like it should do what you're asking. I've used Panorama Factory and it works pretty well, but it's a PC-only product. I'm about to switch to a Mac-tel when the new ones come out, it then it should be straightforward to use PC software on the Mac.
Also, have you tried just using the stitcher built into Photoshop and Photoshop Elements? It works pretty well. If you don't have either of these, it might be worth getting Elements just for the stitcher and considering the rest of the package a freebie!