I did P90X about 6 months ago. I loved it. Here are my few tips........
1.Set a time every night to do it (or morning, but night is better for me). And flat out DO IT. No exceptions. Even if you don't want to do it, tell yourself you are only going to do 15 minutes of it. You will find that once you get to the 15 minute mark, you will push yourself to finish it.
2. Watch what you eat. If you eat the same old crap, you won't see the pounds come off, hence you won't be as motivated to keep doing it. Once you see the lbs come off, that is all the motivation you need to keep doing it, so eat well.
3. Forget the chin up bar. It is hard, especially if you are really out of shape. Just do some push ups instead, or some free weights and lift them when he is doing the chin ups.
My wife and I were doing it for a couple months, and were really enjoying it. Then we went on vacation and when we came back, we found it very hard to restart it. So, and I can't stress this enough, DON"T STOP. If you stop for even a week, you won't want to start again.
No doubt about it though, the program works. Especially if you eat right. I wouldn't focus on the meals they tell you to eat. Just eat sensibly. No fast food, eat more veggies than normal, and eat leaner foods like turkey and chiceken. The lbs will start falling off of you.
Also, if you find yourself losing motivation, I found it helpful and go to youtube and watch the before and after videos of P90X. It can help get you over the hump somedays.