So, got the table bits lashed together and working properly now. Ugly end product that looks like a 7th grader put it together:
And the end result is thus:
Unfortunately, one of the lasers is misaligned, so you still get bright light shining off your thumb when it's not touching the screen unless your hand is at a (completely unnatural) 90 degree angle to the table.
Support is the next thing to work on, then it's time to look at the projection stuff. Ouch.
What I ended up doing:
1) just using the clay to hold the laser and adjust the pitch and yaw, then striped some hot glue across the top to control roll.
2) stapled the wires up along the sides to the top of the frame
3) hacked up quickcam for the shots as noted in previous posts
It turns out that the grooves that I cut were pretty much unnecessary.. the light seems to shine fine if the laser is flush with the acrylic. We slapped wet modeling paper clay into each corner and used some guides to calibrate the beam, and pushed the laser down into the clay until it just about dug a channel out from the front of the laser to about half way back. Then we left the clay to dry for about 20 hours before gluing the lasers in place.
For calibration, we simply used 4 red Solo plastic cups to provide markers for the beam and adjusted the beams by using a webcam with the lights turned down low. We didn't use the modified logitech because I wanted to be able to see where the beam was in relation to the cup. Some stuff I learned during calibration:
1) if the beam appears to be V shaped, it means you've got one side angled up and the other side is a reflection from the table top.
2) the just above the white lip of the cups is about where you want the line to be, or right below the bottom crease on the cup
3) for the line splitters on the laser, you want to make sure that the rough side is facing towards the laser lens, and the smooth side is pointed out. :( Instead of a focused 89 degree arc, we got a 150 degree arc that dimmed the closer you got to the center
4) don't be afraid to drop the camera down under the table to make sure that you've got the laser shining at the right place... ie, test each laser from the under the table POV