As far as placing the light against the plexi, you can pretty much put it anywhere along the edges of the plexi. For mine, for the sake of trying to mount it vertically, I actually put my light BEHIND my plexi, instead of on the edge [you can play around with the placement and see the difference it makes - more light gets into the plexi and engraved areas if the light source is placed on the edge of the plexi]. I basically constructed a 'slot' for my plexi using a couple pieces of angled aluminum and my ccfl light, as shown in the drawing below. As far as using an engraver to do the etching, all I can say is try it out on some scrap plexi first. I tried using my dremel, and wasn't very happy with the results for a couple reasons. Number one is that I couldn't find a bit that would give me as thin a line as I wanted, therefore I couldn't get good detail. Number two is, because of the nature of the tool (rotary) and the nature of the material (soft), I couldn't get a consistant 'cut depth' with the dremel. Furthermore, because I was using balltop bits (generally work well for engraving), the inconsistency of depth led to inconsistency in line thickness. Both could be rectified by using a depth guide (like the dremel router base), but this makes it a little more unwieldly - better for a larger pattern. When I get around to it, I want to make a sign for my arcade room, which I'll use a dremel for, and I'll post up my results and any other tips I pick up while doing it. Be sure to do the same!