I have been fighting with this problem some time ago. Converting gerber to G-code isn't that easy. If you are running on linux : http://gcam.js.cx/index.php/Main_Page it seems to be a good solution.
On the other hand I have seen that newer versions of kicad can export to DXF, here you can find easy an convertor from DXF to Gcode. Good luck, and tell us too what solution you have used / found. Daniel
