Just curious Marty, what are you planning on making?
Fania has a good idea if you can find the center of the CD. 
OK. 
Say you try Fania's suggestion. Here's what I would do:
1. Trace center hole with a pencil on a piece of wood or something similar.
2. Draw 3 diameters across the circle as best you can by eye.
3. If you did a perfect job all three lines will intercect in the exact center of the circle.
4. Position the CD over the circle of the hole you drew. Fasten it down with tape or clamps.
5. Use Fania's gadget or equivalent and cut out the ring you want.
