It sounds like what you want to cut is 2.5D, not 3D:

http://www.welsoft.co.uk/machmill/hs20.htm

If it's actually 3D then you may well need the model as an *.stl file as most CAM programs accept that.
For 2.5D the free edition of Cambam (http://www.cambam.info/downloads/) is good, or Vcarve and various software by Vectric.

But it looks like you're after something that does this automatically from a 3D model. I don't think you'll get that without spending a lot.