Tip for you mate, when you get started - weigh yourself once a week. A few folks that I know that used to smoke put on the pounds "comfort eating".
Fly, Pete is right, you have to be careful not to replace one "addiction" with another. My wife "gave up" a couple of years back, but repaced the fags with those electronic type fags. So she does have some of the benefits, they aren't as bad for your health, not smelly / dirty, etc, but she is not much better off financially and the nicotine still has a grip on her.
Still, its a first step which is positive. Slowly slowly, catchy monkey, as they say. Good luck.
