If you're really interested in some great boxing info, find your local library's interlibrary loan program, and search out a copy of Dempsey's book "Championship Fighting". It is the best boxing how-to (in fact the best martial arts book, period)that I have ever seen.
The writing style is old-fashioned, because he published it in 1950, but it goes into great detail about how to punch hard, and the drills to make it happen.
I have put in over a decade of martial arts practice, and this book made my hook punch work, and jabs much stronger. It's good.