Epson had a set of HDTV screens using 3LCD technology. It also had a nice cutaway view to show how the technology works:
The light comes in from a lamp. It gets split into red, green and blue. Each color goes through a small (2-inch by 2-inch), clear LCD shutter. The colors get recombined in a prism and come out on the screen.
For more information, visit Epson.com.