For informed discussion about weight lifting try the
Ladies who Lift forum here at 3FC.
The more muscle you build, the more efficient you become at burning fat. Muscle is more metabolically active than fat, and you will burn fat at rest and become much more efficient.
I have weight trained pretty much from the beginning. For a while my arms especially got bigger (I measure as well as weigh) however, I got loads of comments about how great and slim my arms looked! The muscle helped give the fat some definition.
The advice I got was to keep building muscle, and that's what I have done, and I am really pleased with the results so far.