Thats indeed cool. I was also interested in how this multitouch technology works and came across some articles in web. It is amazing that is really not so hard to build something like that by yourself. If you are interested to build your own multitouch sensor or even display look at this MultiTouch tutorial . Even more resources about open source multitouch can be found here multitouch.nl there you can download this pdf file with more comprehensive guide How to build MultiTouch display.
In general Microsoft is using very similar technique in his Surface Table.
(IMG:
../forums/style_emoticons/default/thumbup.gif)