As a medic i can give u my professional opinion
on this one ... (Versus my usual nonsense chatter)
Don't waste your money, if you are eating a low fat diet (SW) then products like XLS, lipotrim, Xenical/Orlistat/Alli have limited effect.
They work by binding approx 1/3 of dietary lipids and send them out of the body and down the toilet, usually noticeable on the surface water in the loo as oily drops or an oily film.
Unfortunately these drugs have pretty grim toilet side effects and more or less force you into eating healthily (SW!) and you end up learning a lesson in what not to eat.
You have the SW books/web/app/clubs/forums - this should be enough to help learn what you can eat to lose weight.
(Can you tell I really like prescribing these things?!?)