Thanks guys

And Het, thanks for the link!
I don't think waiting to see if he gets de-sensitised is an option as his reaction is quite severe. He can stay in a two-cat home for about two hours before he has to leave.
It's quite sad really as he really does love cats.
My friend has a Siberian cross called Calder (I don't have any pictures of him but I do have a few movies of him hosted
here). Unfortunately Calder lives in Las Vegas, so stealing him is not an option, but I do know they are lovely, good-tempered, intelligent cats.
I'll rootle through the internet for more information and hopefully have a success story and pictures for you guys in a while... Will take a while, especially as he'll have to wait for a kitten if he is indeed not allergic to them, but I'll definitely update you guys when I know what's going on!
Thanks for the help again, you're a truly lovely, helpful bunch!