After Johnny Lee (Carnegie Mellon Grad) came up with his $99 Wiimote-based interactive surface, several industry solutions propped up as well. The latest one is from Chief (we use their projector mounts): combined short throw mount and mac/pc compatible interactive bundle that can turn any board into a smart board:
http://www.proavmagazine.com/mounts/chief-ships-interactive-mount-bundle.aspx?rssLink=042711-Chief+Ships+Interactive+Mount+Bundle