Marks has a good blog post up with an embedded video of Mike Tyson training. Check out the video and Marks' commentary about it; it's worth seeing.
I might disagree with Marks about whether Tyson "was the greatest boxer to step into the ring." Then again, I might not. These are fun debates to have over a few beers with friends, but as far as answering who was or is "the greatest," I find the debate itself is a lot more important than whatever conclusion one reaches (which is bound to be different from the other guys talking about it).
It's helpful and inspiring to see a masterful presentation of some of the things my coaches have been trying to get me to do over the years.
Also, I hope you'll spend some time at the rest of Marks' blog. He has a fair amount of boxing content, along with the various other martial arts and MMA.