Arduino mill and RAMPS 1.4 What software to use?

I am basically new to the Arduino world. I can execute basic commands like making things blink or tripping a relay. What I am attempting to accomplish now is a 3 axis cnc mill. After a bunch of research I decided that the Mega 2560, RAMPS 1.4 shield and StepStick stepper drivers. I did buy the SD add-on for the RAMPS board. Making use of it would be nice but at this point I feel that leaving it out would be fine. I am not confident in my own abilities at this point to code modify for use if that was required.

Now that I have this stuff I am finding that I overlooked the fact that all the documentation I found was for 3d printing machines not for material subtraction. So I am stuck and am looking for guidance to make this work. I am hoping to do this all in open source and run under the windows environment.

So I am stuck on two questions...
What G-code interpreter/uploader I should use? or does it really matter?
What firmware do I need to put on my mega to use the RAMPS board?

What G-code interpreter/uploader I should use? or does it really matter?

The G-code interpreter is the same if it is removing material or adding it. What changes is the G-code generator.
The same goes for the uploader.

What firmware do I need to put on my mega to use the RAMPS board?

Any software that will drive it. I believe there is a ramps software on the rep rap site but most can be configured to drive it. Just look at the configure page of the software and get the # defines right for your board.

I have written some stuff in processing you might like to look at, you can run the processing language on any platform:-
http://www.thebox.myzen.co.uk/Mac_Apps/Processing.html

It was to go with this project:-
http://www.thebox.myzen.co.uk/Hardware/CNC_Conversion.html

Grumpy_Mike, Thank you for your post. Your comments are most helpful. The firmware issue was the biggest thing for me that I had trouble understanding. It makes sense that the firmware should all drive it. If there's no extrusion code it just wont do anything with it. Just pick one and make sure the write pins are correct.

Now onto the issue of finding the right G-Code generator and uploader. I think I found one for linux but I would still like to find an open source application for the windows environment.

You have to pay but Cam Bam is very good and not too expensive.