I would've thought a 2.5" drive would've been more sane to try first off but, meh
Personally I don't see the appeal of doing it really. This said, I have the urge to look up 1.8" drives now; could be really useful to fit one where a standard 2.5" or 3.5" would be too much.
No doubt probably a special order because if I remember they're special made for the iPod, but that said given the number of iPods in ciriculation you'd think the price would've dropped. Well anyways interesting, but still can't help but think some people have too much time on thier hands ^_^