There is already some great advice in this thread. You should consult your doc before starting on any work out program or major diet changes. There are no short cuts in healthy weight loss.
Ive recently started to get fit. I was about 250lbs (6'2") feb or last year. The first thing i did was stopped drinking soda and cut down on my beer intake substantially. The biggest thing i did and still continue to do is change the way i eat. I never used to eat breakfast. Now its my biggest meal of the day. just changing my diet helped me drop 25lbs in a matter of months. I eat my biggest meal in the morning and my smallest meal for dinner. Lots and lots of water. Cut out the fried foods and started eating more whole nuts and more vegetables.
I had not done any training until 3 months ago. If you want to do cardio, do high intensity interval cardio. This will help you loose weight more than just running miles and miles. Cardio is an inefficient weight loss method. You could also just set a steep incline on a tread mill and walk at a brisk pace for 20 mins or so.
I started following the Strong Lifts 5x5 program. Since starting this, my posture has improved and so has my strength. Its a simple program to follow. and it is completely free. It involves compound movements. Squats, Overhead press, bench, Rows and Deadlift.
I am now down to 196lbs and hope to loose another 10 or 15lbs of fat and replace that with muscle weight.
Look up a calorie metabolic calculator to get an idea of how many calories you need to take in every day. Something like this. http://walking.about...l/blcalcalc.htm
The hardest obstacle i faced was mental. You cant see a "diet" as a temporary thing. Your diet is what you eat every day. You might have a diet of fried food and candy or a diet that has no red meat, whatever it is that is your diet. People get caught up in thinking that they go on a "diet" thus making it easier to fall back into bad eating habits. This is a change of lifestyle you need to make, there is nothing temporary about it.
Also when you start working out and are having a hard time at the gym or w/e you end up doing, never ask your self "Why am i doing this to myself, why am I punishing myself, this sucks" Your mind set has to change from a victim to a person of action and positive outlook. No more "f*#k i dont want to run 2 miles today" and more like "Im gonna kick those 2 miles in the nuts!!"