The best exercise I know for burning fat is cycling. Running burns more per hour, but you can't keep it up for as long. You can buy turbo-trainers or rollers so that you can turn your bike into an exercise machine. They have a reputation for being very boring, but perhaps you could do it while watching telly. Im afraid you would have to do an awful lot of exercise to make a dent in your weight. There's about 3500 calories in a pound of fat, and cycling burns up, on average, about 600 calories per hour. You'd still have to watch what you eat.
any ideas?