The first two weeks can see a quick weight gain but much of this is due to a bloating effect that accompanies smoking cessation. This water retention effect is normally subsides sometime by the end of the second week.
Weight gain that happens after this is more likely going to be due to a change in dietary patterns than it is from a change in metabolism. We have a number of strings addressing the weight control concerns and that talk about how to minimize the gains and how to actually establish eating patterns that are conducive to losing weight.
Freedom though is a smoking cessation site, not a weight control site. If people are interested in weight control support groups there are plenty of them on the Internet, although it is probably best to talk with your doctor have your doctor refer you to a nutritionist for dietary counseling if you are considering any major dietary changes after quitting smoking.
Our only position on weight control is that it is possible to quit smoking and to stay smoke free even if you pursue other lifestyle changes--weight control efforts being one of them. To stay smoke free even when watching your weight is as easy as sticking to your commitment to never take another puff!