If you're a woman and you're only doing aerobics and maybe some light machine work with little struggle, good luck, because you're not going to get anywhere (well, initially you might, as I've mentioned before, nearly any exercise "routine" works for a little while (see Philosophy)). News flash, aerobics do not "tone" or "shape". Aerobics burns fat, plain and simple. Lifting weights like you mean it helps build lean muscle mass, actually turning your body into a more efficient fat burner at the same time you're changing your body's shape. Combine this with fat burning aerobics (not excessive mind you) and you'll look awesome.
Even if you wanted to, it's very difficult to put on significant muscle size. It takes years of consistent and hard bodybuilding movements combined with the proper diet. You have to really want to get like that ("too" big) to get like that, plain and simple. Hormone-wise, women (those that don't take steroids) don't really have anywhere near the testosterone levels necessary to ever become "huge". If you throw away old notions, you'll make gains like never before and look drop-dead gorgeous. Also, don't worry about "losing" your breasts, as that's another fallacy. Breast tissue is made of fat, and if you were on the kind of low fat diet that is required to "lose" breast size, then you obviously know what you're doing (and what the truth is) and wouldn't need my two cents.
