Usually the cause of pain in your wrist from using a mouse and keyboard can be traced back to the way you're seated. You want to make sure that your desktop is the proper height and distance relative from your body when seated. Make sure your forearm is fairly level with the desktop without any awkward adjusting or strange angles. Have the rest of your arm in a relaxed decending position.
Proper form will help allieviate pain. Also, try looking into wrist rests for your mouse pad. If you still experience pain, then you might want to take periodical rests from the computer to get up and stretch.
Good luck, and I wish you good health and computing =)