This is an even cheaper version of the cheap multitouch table originally made by cerupcat. Unfortunately it doesnt seem to like me or my hands (extremely cheap) but you might have better luck ;)
Sorry for the lack of pics but i didn't take any until i had already made it...oops.
Step 1: Stuff...
1 x Box (my stereo came in the one i used)
Enough tracing or baking paper to cover the top of the box
Knife or scissors
DUCT TAPE!!! ; )
Step 2: How to...obviously...
2. Cut hole in the side of the box to feed the usb cable through
3. Place your webcam on the bottom of the box facing upwards and secure it with the almighty DUCT TAPE!!!
4. MAKE SURE!!! That the camera faces EXACTLY UPWARDS towards the top.
5. Feed the cable through the hole in the side of the box and ensure that it doesn't move the camera.
6. Staple the paper over the top of the box once you have finished everything on the inside.
7. Seal up any open areas with duct tape.
8. Download and install MTmini Software Package v1 off this site
9. Calibrate the pad and HOPEFULLY it works properly.
This took me about 10-20 minutes.
Also you can draw a square in marker pen on the paper to show where the camera actually senses isn't needed but helps.