This thread is probably dead, but some exercises would help prevent some of the soreness. Any continuous repetitive motion is going to cause strain on the muscles and tendons, no matter what part of the body you're talking about. (You usually hear about the wrists, the neck, and the back.)
The trick is to make sure you work the opposite muscles as well. When you have your fingers on the fretboard you're curling them inward. Take a break every so often and flex them backward, use your other hand and hold them back for about 30 seconds at a shot, don't push too hard or bounce the stretch though, this could cause other problems. At first your fingers probablt won't want to stretch too far because you've overdeveloped the muscles that you use when playing. Be patient, eventually they will loosen up. Remember to work on your wrists, elbows, and shoulders too.
If the pain starts kicking in during your practice sessions, put the guitar down and give your body a break. You might want to try some type of linament(like Flexall 454) after you're done playing whether you're hurting or not. If you're developing tendonitis you'll have to stop playing for awhile or you'll do permanent damage. You might want to consider seeing a doctor if the pain doesn't go away soon. You definitely don't want to jeopardize your ability to ever play again.
