In reply to hugedyno: it depends if your looking to improve stamina or maximum strength..many long ones for stamina(eg. 10 reps of 20sec hangs and 40 secs rest, up to 20 reps, then back down to 10 and increase hang time and shorten rest, i.e always 60 secs each rep, then more reps etc.) of and many ones short for max power (5 reps of 3 secs rest again, you know the drill, start adding weight when it gets too easy etc). :0 obviously its a bit more complicated then that, almost at least but thats the main jist of it.
get Eric J Horts training for climbing, has some good tips, or go to
http://www.trainingforclimbing.com/ has some stuff as well on the subject.