The folks at Maximum PC made their own multitouch Surface system:

It all started while we were researching an article on future user interfaces. Touch interfaces are hardly futuristic at this point, but multi-touch hardware like the Microsoft Surface or the iPhone is just starting to become a big deal, and we decided to see what big things are going on in that field. What we found that surprised us the most wasn’t anything about the future of multitouch; it was about something that people are doing right now.

There is, it turns out, a whole community of very smart folks out there on the internet perfecting the art of building DIY multi-touch surfaces. The process isn’t exactly simple, but the results we saw were stunning: multitouch surfaces with responsiveness rivaling Microsoft’s $12,000 offering, built in a garage on a shoestring budget. “Future UI article be damned,” we thought, “we’ve gotta build one of these for ourselves.”

Build Your Own Multitouch Surface Computer