Ok here is a really cool post you do not want to miss. Using just a Cardboard Box, a low cost Webcam, a Piece of Clear Flat Sturdy Material and a paper, build your own multi touch pad in less than 5 minutes. So how does this work;

It’s really easy and simple. It handles tracking blobs of infrared light, and sends your programs these multi-touch events, such as 'finger down', 'finger moved', and 'finger released'. It includes a configuration app and a few demos to get you started, and will interace with most types of webcams and video capture devices. It currently works only under Windows but efforts are being made to port it to other platforms.

See the video demonstration>>
Visit Touchlib Website>>