You may already know Jeff Han and his multi touch finger tracking, if you don’t go here: http://cs.nyu.edu/~jhan/. With a small acrylic pane, some IR LEDs a video projector and a webcam that we modified to see IR light we built our own little multi touch display. It actually works really well.
This is a picture from the IR webcam. The bright spots is where the fingers touch the acrylic pane.