A DSI (Diffused Surface Illumination) Multi-touch surface uses a special kind of acrylic called Endlighten that allows IR light to be diffused across the surface of the acrylic. What's particularly cool about this set up is that it will also allow for the use of fiducials (such as barcodes) on the surface of the table.
Peau Productions has a great intro into the whole setup.
For all things open source on multi-touch check out NUI Group - especially the forums, most of my questions up to this point have been answered there.
Shopping list for 1 multi-touch table
Notes on UTS DSI Build
Notes on Critical Making Lab DSI Build
Projects
http://www.achter-sinn.de/multitouch/ this is a cool short blog by someone who created a complete DSI multi-touch table from scratch.
http://tel.dur.ac.uk/synergynet/ this is the research page from the Durham England team that developed software for passing objects (data) across multiple surfaces, and cross-surface collaboration. Definitely worth checking out the videos.
http://www.intermedia.uio.no/display/Im2/Home the Oslo team that we're working with, just a cool site in general but there are several things in the project pages worth checking out
http://www.stellarnet.eu/programme/wp3/rendez-vous/tabletops This links to a series of talks on tabletop computing that took place this fall in Switzerland. A collection of the abstracts can be found here
Software etc.
Here's a link to the NUI Group's page on their latest build of their multitouch for java. From the site it says that it is completely compliant with Windows 7 and integrates with its native multi-touch capabilities (the link to the Google code for the software is at the bottom of the page or you can use this link)
Also check out here its an outline (by Peau Productions again) on all the different layers of software that the table will need.