P90X... What do I have to do to be prepared?

Okay, so I'm 22 years old. I weigh 190 lbs. My body fat percentage is around 23%. I haven't been active in any sports or workouts for the past 8 years. My body, surprisingly, doesn't really reflect the way I live my live. I eat Bullshit, I don't work out, I smoke... but I'm only 190 lbs when I feel I should be around 250 lbs. Anyways, with that said... I've finally chose to make a life style change. I've decided to do the P90X workout. What am I getting my self into? I'm not going to purchase any kind of supplement or nutrition plans from them directly... So what kind of supplements should I use? What kind of foods should I be eating? How many times a day should I eat? Yes, I'm absolutely sure I want to do this workout. I feel like I should change the way I'm living my life before I end up with diabetes, or become too obese...etc... Any thoughts or suggestions would be great. Thanks.