Try mach2
It has a free demo limited to about 100 lines of g code and has excellent backup and updates.
Author at:
http://www.artofcnc.ca/
support at:
http://groups.yahoo.com/group/mach1mach2cnc/
This handles 3d with no problems and runs from winxp,And im sure that it's only about $150. to reg.
Mark
http://website.lineone.net/~rmtucker/