There is a CNC cape available for use with LinuxCNC - more info from this very forum here.
Essentially, RPi, Arduino, BB and probably any other Single Board Computer or Microcontoller has the capability of driving a Laser Engraver. If you can produce X/Y drawing commands to steppers and turn a laser on and off then you just need software to take your design and convert it to those drive signals.
Do as I did, google it (I often end up linked to instructables or similar). Many have gone before with this project, no point reinventing the wheel here.
I'd say your biggest challenge is going to be deciding on which software package you get on best with.
