Here we look at building a multitouch setup using an infrared light source to light up fingers/objects placed on the surface and a camera to track the blobs....
Multi-touch interface (from Adobe TED)
How To Build a Multitouch Table - Part 1
Multitouch wall Cleveland Museum
How to Make a Cheap Multitouch Pad - MTmini
How to build your own multitouch table?
06.- Curso de Android. Eventos Single y Multi Touch.
Low-Cost Multi-touch Whiteboard using the Wiimote
Dell S2240T multi-touch monitor