dunno, i guess it should be (everything is limited there). But the origamis are (at least now) completely useless.
They are slow, dont have a keyboard that can be used to tipe anything longer than e-mail (the handwiting recognition is still not developped far enough
(I was once lended out a tablet pc from my friend and it couldnt read my writing (it is pretty crappy - take a guss why i type everything out) , so it was faster to tab the virrtual letters with the pen)),
have crappy battery time (even the laptops wizh P4m seem to outrun it), have tiny screens, ... (you get my point) (note - i'm just relaying information on the origamis - i never even touched one)
So: stay away from origamis, only use Tablet pc version if you have a tablet pc - and can get along with it
Therefore use XP pro or if you are looking for a slight performance increase (especially for low end/battery conserving laptop (sell than 0.5 GB ram, slow HD & processor)) win 98 Se (never had ME - can say anything about it) (and if you can find all the drivers/progams you need/wamt)