You don't have to give up beer to lose weight. Regardless of the diet plan, it boils down to calories. The reason diet plans cause you to lose weight is because they restrict calories. That's it.
I've seen the P90x infomercials and they look like a pretty good exercise program but I haven't looked into the nutritional side of things. If they give you hard restrictions like "no beer" or "no this" or "no that", I would throw it out. Not that cutting out certain things is entirely bad, but because you really want to find something you can maintain and be happy with over the long term.
At the beginning of the year, I started at about 230 lbs. I'm now under 195. Here's a graph of my weight:
That's pretty consistent weight loss at a very healthy 1lb per week. I've had beer every single day. I haven't gone hungry a single day. I haven't cut a single thing out of my diet. I've made a few adjustments to balance out my macronutrients but other than that, I eat what I like.
I had already been going to the gym for 3 months before the end of the year but I had actually gained weight during that time. The weight started to come off when I started tracking my calories. I use Calorie King (which is kind of pricey) but there are plenty of other sites like The Daily Plate (which is free) that let you track your calories online. Once you get the hang of it, it's super easy to do.
Ultimately, you need to find what works for you, but for me this has been the only thing I've ever found that gives me total control over my weight. If I want to lose 1lb per week, I eat 1900 calories per day + whatever calories I burn exercising. If I burn 500 calories on the treadmill, I can eat 2400 calories that day.
If I want to maintain my weight, I eat 2400 calories per day + whatever I burn exercising. It's dead simple.