Sony just recently released a new small PC, and this time they've almost reached the size of a large PDA. And it runs Windows XP! The U50/U70 is only released in Japan and I think even if you can get one and install English XP on it, it'll be difficult to get the drivers and applications that comes with it. Its not a tablet PC, as in there's no Windows XP Tablet Edition but Sony seems to have included some proprietary software to make it easy to compute on the move without a keyboard. There's an external keyboard in case you find that table to set up the whole thing.
Prices in the US seems to be around $2500 for the U70, which is much steeper than the previous Vaio U1 which sells for below $2000 when it was released.
Alternatively, it seems companies such as FlipSTart and OQO are coming out with MiniPCs as well but so far Sony is the only one on the market. Its going to be an interesting 2004 if more companies come up with one, and the price point reaches something around the price of a highend PDA... at least now I can justify upgrading my 2 year old Clie NR70V! Maybe I'll have to wait something like another 3 years for that to happen.