The treadmill is a great piece of exercise equipment, so do not feel like you're not going anywhere with it... heh. Sorry.
I walk on the treadmill at the gym almost every day, and the thing I like about it is that you have so much flexibility. You can increase speed, distance and incline to vary your workouts. Shape magazine has a different treadmill workout in it each month, which is great if you're just starting out and need help figuring out what the heck to do on the thing.
Nothing sculpts your legs like running... nothing. And talk about a calorie burn... it's amazing. Be careful about taking the "calories burned" from the treadmill readout as absolute, because different machines really vary. I have found the elliptical to say I've burned almost double the calories that I really have.
If you're serious about keeping tract of your calories, and carefully measuring your intake and output, invest in a heart rate monitor. You input your specific info and then the readout tells you calories burned for the duration of whatever activity you're doing.... housework, running, walking, cycling, weights, etc. Then, if you keep tract of your calories with the food diary on this site, you can really see what you take in and what you burn and where your weight loss will be. Such a great tool.
Good luck. You can do it!