Like someone said, you can't choose where you lose your body fat. That's up to genetics. What you can do is slim down everywhere and rebuild muscles where you want. Make sure you don't try to do both at the same time. It can work but it'll take longer. When you lose weight, you'll always lose some muscles as well.
As simple as this answer is, it's the truth. The only way to lose belly fat is to lose "overall body fat" by doing daily cardio. You cannot target fat loss. P90X is a great program. If you follow it for 90 days, you should definetly see some fat loss because they incorporate a lot of cardio such as Plyometrics, Yoga, Kenpo, etc. Keep at it, and keep doing cardio. Try your best to cut down on junk food and eat healthier.
He's dead on. I've lost 17 lbs (9% of my total weight) in the past 5 weeks on diet and moderate exercise. I eat 5 400 calorie meals a day and I walk to work instead of taking a cab (basically adds 2.5 miles of walking a day)