After doing some more reading and watching the arbitraious's laser table demo, I'm pretty much sold on trying that out first. Aside from the fact that mounting 4 lasers sounds like a much easier task than 40 LEDs, it also sounds like the laser approach offers up better responsiveness. The lasers are slightly more expensive (around $8 per, whereas the LEDs are about $2.63 for 10 for the high end ones), but that's not really the major cost center of this project.
Plus, I'm sure that by simply ordering lasers online, your name automatically goes on some FBI watch list, so... +notoriety, amirite?
For the video camera, I'm planning on grabbing a $20 Gigaware 1.3MP cam from The Shack (looks like a flat disk... avoid the one that looks like a mini-quickcam-eyeball-with-a-bump-on-it) simply because it's so low profile.
The sticking point is what to use to actually project the image. I don't want to waste money on another projector, but TheDude pointed out that some of the pico pocket projectors are around $200 and designed explicitly for short throw distances. The other approach might be to just tear apart an LCD and get a fresnel lens. Still mulling that part over. It'll affect the height of the enclosure.
I'm also mulling over the construction of the frame to hold the acrylic sheet. Trying to decide if there's a way to have it hold the lasers in place without having to muck with the sheet itself, and looking for some IR absorbing material to line the insides with (for that token nod towards "safety"). Will probably start ordering parts tomorrow and see how it goes.