I am a special ed teacher. I suggest you read up on the disorder. Here's a good place to start: http://www.cec.sped.org/Content/NavigationMenu/AboutCEC/I...
or go to www.cec.sped.org, in the search box type "ADHD" and the first listing is US Office of Special Education Programs study that details the disorder and how to teach kids with it. While its focus is on the classroom, the same principles apply at home.
A highly structured routine environment is a must. Kids with ADHD need clearly defined limits that are reasonable at the same time. They may resist at first, but ultimately they also feel out of control and structure and routine help them gain some control. Do understand that his impulsive behaviors are just that and that while for most of us, we have the ability to actually think before we act, ADHD folks don't have that filter. This does not mean that they cannot learn it, and the time to start is now! Be explicit about what the rules, boundaries and social codes are. Do not assume he gets it but chooses not to because its fun to be out of control. He doesn't and it isn't.
ADHD kids tend to be really smart and easily bored, but unable to focus on one thing at a time. This causes them to fall behind in school.
Another great site for gaining understanding of what it is he is going through is: http://www.pbs.org/wgbh/misunderstoodminds/ Go through the attention activities to get a glimse into his world.
Regarding all his energy, get him in sports. Give him appropriate places to let all that energy out. I would steer away from meds as much as possible, and look into it as a last resort. There is also research out there on diet. Interestingly, for some caffeine can actually settle ADHD people down. Not pop, cause of the sugar, but tea or coffee or something. Do some research and see what his doctor says.
I hope this is helpful. Remember your stepson to be is no doubt a uniquely gifted little guy who just wants to feel loved and secure and able to be in control of himself, even when he is most frustrating. Anger, though we are all tempted, will not help him.