Johnny Lee (of the Human-Computer Interaction Institute at Carnegie Mellon University) shows you how to create a cheap electronic whiteboard system using the Wii remote. Basically, the Wii remote is a Bluetooth device. It has four IR cameras on it, and if you use a Bluetooth-capable notebook or PC, you can use the Wii remote as a tracking device for any IR source in the field of view of the Wii remote. If you attach a IR LED on top of a pen, the IR pen can be a "mouse" of sorts.
No Wii required. You'll need Johnny's "Wiimote Whiteboard" software, available for free at his website via CNET Asia. His website includes additional Wii projects.
Make your PC/LCD/Projector screen a touchscreen with a Wii remote - reHASHplus - CNET Asia