Wacom has posted their vision of Wacom Pens and Vista whether using a pen tablet, pen display, or Tablet PC.
Vista is designed to allow users to get better results in less time and to help make that a reality they are introducing extensive support for pen and touch input. As the global leader in pen input technology Wacom is dedicated to this initiative and actively collaborating with hardware manufactures and software developers to support this vision of universal pen use. When you work on a Vista machine with a Wacom pen (pen tablet, pen display, or Tablet PC) your experience includes powerful note taking, handwriting recognition, and fast navigation options that allow you to quickly and intuitively get the results you want.
Intriguing that if you follow the link to Vista Drivers and select Tablet PC the only driver available at present with XP. Other tablet types have Vista drivers available.