sandman - that trackball is the wrong one to get.
Get one that uses your thumb.
I use a mouse all day at work on a CAD machine and my hand gets somewhat stiff by the end of the day. At home I use a
Logitech Cordless TrackMan Wheel Mouse and its TERRIFIC for comfortable computing. Its a much more natural position for your hand than that damn marble mouse (which I have used also - and it strained the tendons on the back of my hand).
If you insist on using your fingers, one that better fits your natural hand position would be better -
like this one.
They do suck for FPS games, because if you spin the ball too fast, the system just ignores it 'cause it can't read the dots. But for every day computing, it works great. I just cross my arms and nestle the trackman in the crook of one arm and use it with the other. Extremely comfortable.
Whatever you use, make sure your elbow is supported when operating either a mouse or trackball. Don't push on the wrist or "bridge" your arm between your wrist and shoulder. THAT is what kills your wrist.
BB