Hi,
I have managed to lose over 8 stone(in approx 8 months)by healthy eating(sort of following the general principles of Slimming World, which is healthy eating by any other name)and by walking. I started out walking slowish and for a little bit at a time and eventually worked up to fastish and to my current weekly total of 5 1/2 hours a week, or more(split up approx 4 x30 mins and 3x 1hr 10 mins). I find my MP 3 player is invaluable. Walking to fast tracks mean you walk faster without realising it(and it distracts you from the pain of exercising/the gasping for breath/boredom etc, hee). I also download audio books, which I love listening to.
I reckon I have lost double the amount that I would have, just by dieting(yes, I have dieted before but never bothered with exercise). I am hoping that this will be the secret to long term maintenance.
Good luck!