I want to clear up a few misconceptions that are in this thread.
First, weight training will not make you "bulky". Muscle growth is controlled largely by the release of testosterone, which women lack sufficient quantities of to become bulky. There are a few (and I do mean few) women out there who have a high level of testosterone and look a bit manly naturally. Those women can become bulky, but if you don't have it already, you won't get it. Don't fool yourself, the large bodybuilder women you see are on steroids.
I have quite a few women clients, none of whom are bulky. This includes the 5'2" 119lb woman who can deadlift 200lbs.
Second, fat burning is NOT a result of the calories you burn during exercise. The "fat burning zone" chart you see on cardio equipment is garbage due simply to the fact that it ignores post-exercise metabolic shift. By the theory of the fat burning zone, you lose weight best by sitting on the couch watching tv because you burn 55-60% of your calories from fat at rest.
Try this just to prove how significant post-exercise metabolism shift is. Check your pulse at rest. Then hop on an exercycle for 45 minutes and stay around 60% of your max hr. Then check your heart rate immediately after exercise and again 15 minutes later. You'll find that your hr is already back at its resting rate. Now, on another day, do intervals for 20 minutes attempting to meet or exceed your max hr. I've seen my hr stay as much as 50% elevated 90 minutes after I finished working out. 20 minutes at 100% of your hr can increase your metabolism for up to 14 hours.
Lastly, the bad news. There is no such thing as spot reduction of body fat. If you lose fat, especially if you have a good bit to lose, you will lose a good bit of boob size. They are made of fat and sinuses.
The only thing that will honestly and truly give you the body you want is proper diet and a mix of resistance training and cardio.
