I imagine that it probably uses a 2.5" laptop HD which could easily be upgraded to 160 or 200gb.
I think my room mate and I are going to get one of these in the new house.
Edit: And because of the fact that it runs on a Pentium M that probably means it has a ZIF socket like the Mac Mini does and the proccy could be upgraded Wonder which chipset it has in it, if its Core Solo compatible that would be sweet.