Dyne... a Powerbar and water for lunch? That doesn't sound like enough... a salad or a sandwich (whole wheat bread, not white) would probably be a good choice as well, wouldn't it?
Anyways, my dad bought the Body For Life book, and followed that program (
www.bodyforlife.com i'm assuming). It's a 12 week program that teaches you how to adjust your lifestyle to a healthy one. If you have good willpower, it works extremely well, as it gives you one "free" day a week, without exercise and you can eat whatever you want. My dad lost 40 pounds in 12 weeks, which is awesome because he was 49 at the time, and quite overweight.
Really, it's just a matter of staying active, cutting on snack foods, and eating lighter. It's easier to say than do, but with good willpower, you can do it. "Dietting" isn't really the right term for it, since you should just plan on changing your lifestyle permanently rather than just for a few weeks time, otherwise you'll just go up and down in weight all the time.