Okay, here's what I did:
First, I took the original image that I wanted to "tronify" (keep in mind these are TGAs in Blender. I just made them JPGs for the web).
Then I made a mask image. Everything black in this image is what will allow light to shine through.
I put the image onto a plane with "shadeless" turned on so that I didn't need to put lamps in front of it. I positioned a lamp directly behind it.
Unfortunately, because I'm still not exactly a wizard with Blender, that's as far as I got. The end result is rather dissapointing.
Obviously the light is getting through. I set the "world" up to be pure black (0,0,0) and the lamp up to be pure green (0,1.00,0). Seeing as the transparent parts of the plane turn out green, that's a good sign.
What I need to do now is figure out some manner of making the light more visible, either by adding "mist" (which hasn't worked for me yet, or something else.
If anybody has any ideas on getting this to work, I'd love to hear them. This has become somewhat of a quest for me since I came up with the idea. I've made it "...this far."