Some tips for overcoming RSI.
Swap hands and input device
Periodically swap input device between your right and left hands. Also, I found that changing the type of input device helped a great deal. Periodically swap between a normal mouse, a finger controlled trackball, a thumb controlled trackball, a tablet, etc.
The problem you'll have is that once a pain starts, switching will get rid of it for a bit but then it'll eventually come back again.
Take regular breaks
Take regular breaks. There is no hard and fast rule for how long - it's all about finding a balance. Start with short break intervals and a long break time. Reduce the interval and increase the break time until the pain goes away, then gradually increase/decrease until it returns. Then you'll know the best times for you.
There are plenty of applications you can install which will remind you when to take a break. Workrave is a good one: www.workrave.org.
Good posture
Posture plays a large part because it effects the potition of your arms, hence wrists. Make sure you're sitting upright with the top of the monitor level with your eyes. Torso and legs at 90 degrees, thighs and lower legs at just over 90 degrees. Most importantly, don't rest your arms on the table - make sure you fingers are the only thing that touch the surface.
There are plenty of diagrams around the Internet for this kind of thing.
I've had much less problems since using a laptop because I use the in-built tablet, though this is obviously not good enough for a designer.
