Well, there's a much simpler way that might just not be as much work in the end: Put the hand footage in an image plane with a locked-off (meaning still, as in not moving) camera. Animate the ring, frame by frame, to look like it's in the right place. Then, in your favorite compositing package, create an animated matte that will cut out the part of the ring that your fingers would be in front of. Assemble the levels together and *voila.*

The only times you really NEED to track in a 3D stand-in for your hand are:

1) When you want to render 3D shadows cast by the ring on your hand (you can often get away with cheap 2D tricks in this regard but you'll need to do SOMETHING in this area to make the composite work.)

2) When you want to simulate dynamics that are affected by the shape of your hand, like moving it through smoke or having something travel along its surface.

3) When the animation is so complex that you really need to have accurate reference for where the body part is. Example: the spyders in Minority Report crawling on Tom Cruise's head required doing 3D roto (the term for matching 3D animated stand-in geometry to photographed objects like Tom's head) so that their contact points would be accurate AND for shadows.

-- Mark