Goal: Pull-Ups

I've set a goal to be able to 10 pull-ups... eventually. I have no idea how long it will take me to work up to it. As of right now I can only do negatives (meaning I stand on a chair, act like I've just pulled myself up, take my feet off the chair and dangle there for a second, and then slowly lower myself down). I did 12 of those this morning plus a little 1/4 pull-up. I only lowered myself part of the way down and then pulled myself back up. I figure if I keep up with this routine and especially keep doing 1/4 and 1/2 pull-ups then I'll build up enough muscle to do a whole pull-up and then 10 whole pull-ups.