I use a fork of the 3D printer firmware called "Marlin" on my Arduino MEGA to control my laser. Specifically, I use a fork by the user Turnkey Tyranny available here. I use Inkscape for all of my design work, as well as Turnkey Tyrannys fork of an Inkscape plugin designed to export G-code suitable for his firmware.
If you have never used the Arduino IDE (software to upload firmware to Arduino boards) before please take the time to go through a few of the tutorials on the arduino.cc website.
Once you have Turnkeys fork of Marlin installed, and the RAMPS board and LCD stacked up, your LCD screen should turn on and look similar to this:
Now you're ready to start plugging everything into the RAMPS board, but FIRST and most important.. look on the RAMPS board for diode D1. You MUST remove this diode before wiring the laser cutter up. It will suffice to just clip the leads and remove the diode, but its a bit of a tight fit so I desoldered it from the back.
If you do not remove D1, then the RAMPS board will attempt to route 24v from the stepper circuits to the 5 volt regulator on the Arduno. It's not rated to step that much voltage, so it will fry and possibly ruin your Arduno MEGA.
Some buildlogs have suggested removing the yellow Polyfuses from the board as well, and bridging their connectors. I did not do this, and have not noticed any trouble even after running the machine for more than an hour one one design. You're mileage may vary. If you have issues with brownouts or the machine shutting down randomly, I would suspect the fuses may be causing some issues.