First of all, I personally hate running on a treadmill. I think it's notoriously boring, not nearly as productive as running outside (since you have a belt that's forcing your feet to move), and I have concerns that it prevents a natural running gait from developing.
To my knowledge, the absolute BEST thing for your heart and overall level of fitness is swimming. Reason being, it uses your ENTIRE body as one giant floating muscle, and you have to consistently move just to stay afloat. If you hate running (especially if you hate running), I would recommend swimming to you.
I also want to stress the mistake I see a lot of women making: Don't go by your weight. I know too many people who think that if they're not losing much weight, they're doing something wrong, so they constantly change diets, hoping one of them will work from day 1. This can shock your system to the point where you make yourself sick, or worse.
Which is preposterous. Your body may be called a "machine", but it's still an incredibly complex system of fibers and chemicals. It takes time for it to adapt to a new routine. In fact, upon initial workouts, you might actually gain weight from new muscle being created. However, exercise is the only method to lower your body's "set weight", the weight which you normally operate from. This is why dieting alone almost NEVER works. Eating right (not less food, and sometimes MORE food, but the
right food) is only one part of the equation here.
My advice to you: Throw away your scale and start judging your body based on how it feels. If you run up a flight up stairs and feel exhausted, that's a bad sign. If you can go up 10 flights of stairs without breaking much of a sweat, that's a sign you're getting healthy, regardless of your weight.
Start small. Swim a little (5-10 minutes). Run a little (5-10 minutes at a pace you can handle). I recommend this phenomenal book:
http://www.amazon.com/Chi-Running-Da.../dp/074325144X
I used to run with shin splints, until I read Chi-Running. Now I might get them once every other month. It made running
easy for me. You don't NEED to run though, as there are plenty of exercises out there, but running is great.
Aerobics are great to start with, as others have suggested. If your heart rate is increasing, your body is working itself! Do some very light, high repe ion weights for muscle tone. Start by working out 15 minutes every other day, and increase when you feel comfortable doing so.
And STAY AWAY from weight loss products. No discussion on this.