Thought some one here would like to wade in for boxing on the comment section of this article in today's NY Times: http://www.nytimes.com/2008/02/28/health/nutrition/28BEST.html?th&emc=th
Does Weightlifting Make a Better Athlete? Boxing makes you a good boxer. Weightlifting is just a small part which can be added to a routine.
As Virus already said, it's a small part of becoming a better boxer. It's just like in baseball, most kids to adults feel that the more they lift the further they will be able to hit the ball, which is not completely true. Practice is key, this means hitting the bags, doing your road work, and perfecting your technique. If you are going to lift weights, concentrate on workouts that help your Boxing, like Squats, Forearm exercises, like wrist curls and rollers, which help with the snap at the end of your punch.