I use a program called ACEconversion, which I got when I purchased my Shearline CNC Mill. Works pretty good, but you do need to check the tool paths when you run it.
I have a Supermax mill with a prototrak MX2 on it. I draw with Autocad 2000i and use Sheetcam (a great program).
I have modified a post processor for the MX2, it workers great.