hey
i lost 20 kg over a longer period of time, but have managed to keep it off- the longer it takes, the longer it stays off!
for me, it was all about eating Low GI foods, foods that make you feel fuller for longer - so you eat less. low GI foods release the sugar from the food slower into your metabolism. its foods like multi grain bread, yoghurts, all that kind of stuff. theres actually lists on the internet you can get which show you what foods are good to eat and stuff. and heaps of great books too!
and in terms of excercise, i used to go for a run like 4 times a week, and played netball...but at the moment, i just use an excercise bike, its great! it was cheap as and theres heaps of work outs on the internet you can use to make you loose weight,
hope this helps!