For what its worth, wrist pain I was experiencing from the conventional mouse disapeared when I started using a combiniation of:
1. A wrist pad
2. Trackball Mouse - the kind you move with your thumb and click with your fingers. http://www.microsoft.com/hardware/mouse/tbo_info.asp

The other kind of trackball, whrere the cursor is moved with your fingers and you click with your thumb did not help my situation for some reason.

Eddie