M.J.
How old is he? Our son was getting medical help at three because his behavior was so extreme (was kicked out of preschool at that age). We started off getting tips from a child psychologist, then moved on to a behavioral therapist and finally the child psychiatrist, who made all the difference in the world with medication.
The AAP just came out and said it's fine to diagnose kids as young as four now, which is going to be so, so helpful. There really are cases, our son included, where the kids are truly a neon sign for having the condition.
I agree with many of the suggestions below. Push for getting the medical help, number one, and also look at the websites for ADDitude magazine and CHADD. Both have really useful information about the condition.
Don't expect miracles. You can try various rewards and consequences programs, but expect them to work short-term. Kids with ADHD aren't going to stay focused on any specific program for a long time. We did a marble rewards jar when our son would have good days at school. He was really, really motivated at first and we made it easy for him to earn rewards (as in, if marbles go into the jar and reach a small level today, you get a reward). But it lost steam over time.
Kaiser had us use the 1-2-3 Magic system for discipline. The concepts were good but just didn't work on our son until he was on medication. It may be worth a try, though.
Don't waste time on dietary changes, ADHD vitamins, detoxing chemicals in the house, or any "natural" supposed treatments for ADHD. It's a brain disorder and the medical specialists are the best way to go. If your child was diagnosed with a vision problem, you wouldn't try to wing it and correct it yourself and the same should apply here. Zero scientific evidence any "natural" paths work (although Omega 3 supplements show promise in mild inattentive only cases ... we're giving them to our son, but honestly not seeing any change, probably because he's an extreme case). Read up on ADHD through reliable sources before taking any steps on your own. You really don't want to be giving your child any unregulated products without being fully informed (supplements such as Omegas included).
If your child REALLY needs to get through an important event, give him a caffeinated soda. Caffeine is a stimulant, so it will help in a child with ADHD. Just be careful about using this too frequently, since caffeine is addictive (unlike the medications) and withdrawl symptoms are no fun (speaking from my own experience giving up coffee).
Best of luck to you as you start down this path!