The trick to making these dove-tail joints is an emery board, the kind for filing your nails. The joints of the project box are laser cut with a "V" shape on one side and a smaller, rectangular hole on the other. The receiving rectangle cut is then sanded down to fit the V shape using the emery board. When assembled, the dove-tails hold the sides together tightly. Screws are added to hold the top and bottom in place, securing the enclosure. I used 4 (one for each corner,) but the box could easily be held together with just one.
The project that I'm making a case for is a modified Sparkfun single cell, lithium-polymer battery charger. The charger comes as a kit for charging li-po's at 100 or 500mA, but with a little bit of tweaking and a few components it can be made into a variable charger.
1/8th inch acrylic plastic. It will work with thicker plastic, you'll just need to do more sanding.
Machine Screws such as 1.25" Length 2-56 Thread from Ponolu
A project to put in the box
Emery Board. These can be found at drug stores and mini-marts.