In July I was 340 pounds, taking 3 different heart medications, was tired all the time and was exhausted just going up one flight of stairs. I'm now at 225, I'm off the heart medications and feeling much better. I still have a ways to go before I'm at where my doctor wants me to be (190, so I have more to lose than you), but I can definitely feel the effects.
#1 - FIND SOMETHING YOU ENJOY DOING FOR EXERCISE!!! I love swimming... so once I closed my pool in the fall, I joined the rec centre and use the pool there three times a week. I get there at 6:30am and swim with the seniors that are up early so I feel pumped up about going faster than everybody there.
#2 - If you can't find something that you enjoy doing, DISTRACT YOURSELF. I have a treadmill and an exercise bike planted in front of my 50in plasma downstairs. I'll throw in a DVD of Criminal Minds and not notice that 40 minutes of cycling has passed.
#3 - Keep a log of your food and exercise. I'm using an app on my iPhone, but pen and paper works just as well. Make sure that you are burning more calories than you are eating. I'm burning at least 1000 more each day than eating. 1000 x 7 = 7000 = 2lb per week.