Search HN, there have been a number of threads on this topic with lots of discussion.

Also, consider that it may be pycho-somatic. No, that doesn't mean you are crazy or the pain is not real it just means your subc mind has zeroed in on your wrists to express conflict (my take). The best book in this area is by John Sarno, Healing Back Pain: The Mind-Body Connection. You can ignore his Freudian rage theory (he wasn't a psychologist) but learn his techniques and you may have success as many people have using his advice, myself included. I completely cured my "RSI" in about a month and can type for hours now without problems.