The OQO is a full fledged PC. It runs Windows XP (Home, Pro, or Tablet PC Edition), and has a Intel Centrino Processor in it (low power version 1.2 GHz, which is faster than it sounds).

It's been rated fairly well, and for an ultracompact pc, you can't beat it. I still prefer them with full size keyboards, that's about the only way to get a lot of work done. But this is an alternative if you need a super small PC running Windows because of a custom application.

(no I don't work for them and have no affiliation with them, I have played with one in the past and thought they were neat, but not something I would want to spend $2000 on, still rather have a sub-compact 12-14" screen notebook).