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:
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.