I find that alot of women (and men for that matter) have their minds set that high reps and low weight is the only way to "tone" or "define." its refreshing that youre actually willing to acknowledge another way. anyway, i think most ppl on this board will tell you that it is most likely beyond your means to naturally become "bulky" or muscular in a masculine way. lifting weights when combined w/ an appropriate diet builds muscle in a pattern determined by your genetics. however, it is true that lifting heavy w/ a rep range between 4 and 10 will recruit more muscle fibers than using light weights and higher reps. of course the words "light" and "heavy" are relative terms for each individual, but if you dont push yourself you prob. wont make steady progress. in addition, its my belief that "toning" and "defining" are misleading as ppl use them - when you lose body fat, your muscles will be more visible. no amount of weight lifting can define a muscle if your body fat doesnt allow it to show. in short, lift heavy and eat clean (check out the nutrition forum) and youll see progress in no time
. hope this helps and here is a site that might shed some more light.
http://www.stumptuous.com/weights.html