The idea itself is “simple” enough. Take the laser with its motor out of CD-ROM and build a connector for its motor so you can connect it to Arduino.
Afterwards you need to build a casing for the motor, and put a mirror on top of it, so your motor can move it. At that point you take a normal laser pointer and shine it towards the little mirror. Reflecting surface is being moved by the Arduino mini-board computer, so you can run the whole thing off some batteries and don’t need a computer.
And that is it. Some more pictures of how the final Laser Graffiti looks like. More hacking continues after the holidays.