Follow other people's advice about "assisted pull-ups." Once you're strong enough, then you can advance to a standard pull-up.
I'm in the same boat as you...only with push-ups. I know I'll catch some flak for saying that I can't do push-ups (or push-ups without devastating soreness for days & days later). But, I've been doing "modified push-ups" as a bridge to a standard push-up so I won't be wrecked for days later.
Good luck!