If the machine still runs VR milling, then it takes a pretty generic Fanuc style G-code.
A Mach 3 post-processor normally works, but it may need a little bit tweaking of certain codes to work without flagging any errors.
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Now you're probably wondering what a post-processor is, but it's the final part of the CAM process.
In a nutshell, you go CAD -> CAM -> Machine code.
CAD can be whatever you want to draw/model in, but it has to output a file format that your chosen CAM will load.
CAM (computer aided machining) is what generates the toolpaths for machining the part. There are lots of options (I'd probably suggest CamBam as it's only demo limitation is you can only load it 40 times before having to buy a license), and most come with some form of CAD element, although some vary from mediocre hair removal aids, to well featured CAD.
Once you have generated the toolpaths in CAM, the CAM package then runs those toolpaths through the post-processor, which is what creates the machine code suitable/specific for your machine.