If using Rhino, use a .jpeg as a source for your bitmap. The bitmap is like putting an object behind glass and then tracing what you see. It has no control except visual control.
Use colored layers to see what you have traced. Then using curves, circles ect to trace the bitmap. Make sure you don't delete your bitmap until done tracing. Adjust curves/lines to make sure they have the correct angle and as close as possible curvature. When you think it is good, then measure (analyze) important parts of your drawing so you can scale it properly.
You can then use the lines/curves to generate the G-code. You could "ordinate dimension" the drawing and handwrite the code or you could use a CAM product to write the code. See the Fall 2011 issue of Digital Machinist magazine.