According to a gym instructor..

I love using the treadmill. And I hate to exercise. I've heard that the best way to lose weight is walking. I'm not one for special diets or calorie counting which is why I myself attend Overeaters Anonymous. But for helping with stress and losing weight walking is the best thing a person can do for themselves. I've been hearing that by fitness experts and Doctors for years. Good luck.

I believe a treadmill will help. Any exercise will help somewhat. However, I have talked to people who have run 5 miles on a treadmill, but found it much harder to do the same thing for real outside. The reason is that the treadmill does much of the work for you and is easier that actual running. For best results, try and run outside on occasion as well.