Unfortunately, it's probably not the weight that has you down.
Losing weight is probably a lot simpler than building up your self esteem.
I know a girl at work who is radiant, and is obese. People hardly notice though because she glows with confidence. She looks more attractive than the skinny chick at work who has her nose up in the air. (God I hate that snobby chick!)
I too have a poor self image, and I'm sure it probably has nothing to do with the way I actually look.