basically photo copy the piece into a cad program.
I usually just make a paper template. If the piece is larger than 8.5" X 11" (my scanner bed) then I'll take it to the 'blue printer' and have them save it as a DXF to my thumb drive, take it back to the shop and clean it up on the computer.
If you have never used a cad, just take it to your plasma vendor and pay him to do it.
you can't JUST photo copy the piece and go. you have to make the 'lines' of your pattern all connected and clean and such. Its the basis for the tool path (the cam side).
Matt

You also might look into the Corel Suite to trace your image. I believe you can save files in the DXF format.

Jake

I have used Illustrator to trace shapes or to produce them for creating a workable cad file to be run on a CNC plasma cutter.
This is great for cutting text because illustrator will let you make vector shapes out of typed fonts that can be exported as a Cad file with no problems.

Make sure that the shapes are closed loops (lines are not crossing in any of the corners) because lines seem to cause problems and loops don't. if you want a line best to make it out of a shape... like a very narrow rectangle.

When you are done with the art save the file as a CAD document.