At least installing the Tablet SDK should add that kind of support.

I think it does, to some degree. You can develop Tablet applications on a regular desktop, you don't even need any kind of pen device. Of course, testing the application is no fun when you have to write with the mouse. And since the handwriting recognition engine is missing, you can't test it all.

I don't know about the Wacom boards, what's their native resolution for the pen? The Tablets' is several times higher than the screen.

Are they pressure-sensitive? Can they check the 'ID' of the pen so an application can assign different styles to different users working at the same time?

The Tablet PC supports all this - check out the .NET Show episode about Tablets.

I agree it would be cool if regular desktops had this functionality, but for what? Tablets are designed to be carried around, and to use them when you can sit down and type or use the mouse. They're very useful to take notes in meetings, but I wouldn't want to have to work with them all day, because I can type way faster than I can write.