Vista looks to add a few new enhancements to the Tablet PC platform. There is some great information in a few PDFs on what the enhancements are as well as some definitions and explanations of a few APIs.
I wrote up a brief synopsis with links to the PDFs here.
I am really looking forward to the next beta release of Vista and so far love the enchancements in the current beta. I just wish I had some real high-end hardware to support most of the enhancements like a dedicated video card with 128MB that has drivers to support some the cool glass transitions, a tablet with a 64bit processor or even better a dual-core 64 bit processor!! :)
Hopefully we will see these devices early than later, but I am sure most will probably be released in conjunction with the final version of Vista...I just have to hold out in purchasing a new Tablet... I hope I can last...