I too experienced wrist and arm pain from prolonged use of a mouse. The solution recommended to me was to invest in a quality trackball. It has made a world of a difference -- pain is gone. I personally own and recommend the Microsoft Trackball Explorer -- it's not cheap (could be as high as $80), but it's changed the way I work. I've even programmed it to allow me to double-click with a single press (it has several buttons, all fully programmable). It took me a few days to get the hang of using it, it's not quite like a mouse, but it was well worth it. Enjoy.

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

One important point that I haven't seen mentioned is technique on the keyboard. Be very sure your posture and your chording techniques are correct. Also, try not to play tense and hit the keys very hard. Your fingering is very important as improper fingering can torque your wrist and contribute to wrist pain.

Al