A few people have asked me how hard would it be to build their own touch table.
Its very easy and the price varies depending on what you already have or dont want.
The video portion is all up the the user. Some people go hardcore and toss in a LCD into the mix and a few people cheap out and use a projector pointing downwards onto the table top.
The table itself. A simple webcam that can support up 30FPS or higher. Two sheets of acrylic, a fist full of IR LEDs, Paper, 2x4s as the frame, power supply, and some metal bits.
The IR LEDs will shine though the thick sheet of acrylic and when you press down it will scatter the light. The webcam will pic up the change and the software will dictate X and Y axis. The Diffuser is nothing more then a piece of white paper or a thin table cloth.
Pretty much any webcam will work. Yet I would recommend to to buy a logitech easycam because you have to remove the IR filter and replace the IR filter with a color filter. The color filter is nothing more then a piece of exposed negative film. This way if you want to add a video monitor or use a projector the camera will not pickup the movement of the video screen. Also comes in handy if you have a celling fan. With out the filter light will bounce off the celling fan and cause movement.
As for software there are quite a few programs out there. For Windows and MacOS X theres a program called tbeta. Its based off of the API called touchlib. For Linux you're kinda on your own. Use the touchlib API and code a program. There are binary premade programs for Linux but they only work so well.