Dan,I agree with Courtney but just to add a little more. I would start with three days a week after your hardest climbing sessions doing a lat pull workout. Do three sets of 40 reps for 2-4 weeks. After that drop down to 8-12 reps at a higher weight for a week or two and start doing pull-ups. Finally, start changing your workouts up. After six weeks start splitting your workouts up into "power" days and "endurance" days. If you can already do 3 sets of 8 or more pull ups then you can skip the lat PD's.
Finally, I have found the "typewriters" excellent for climbing. They are an advanced exercise however and you want to make sure your back is really strong. Make sure you do them slow and in control.