The best kept secret about dieting is that there is no secret. It sucks and it takes commitment. Those books will have you believing otherwise though...
Just some advice, look around for a diet that actually sounds good to you. The best diets, in my opinion, have carbs; they will keep you sane. You'd be suprised the things you'll do when you're deprived of carbs. Also, since you haven't been in the gym in a while, low carbs will make your gym days feel absolutely awful!
If you're feeling really fat, cut the salt out of your diet for a week. The lost water weight will make you feel wonderful and help get you into the dieting spirit.
Good luck.