I study this in University, and to be honest man, this is the biggest misconception. Going to the the gym, or only excercising twice per week is not going to do much of anything for you. You would be much better off doing cardio for simply 20-30 minutes a day.
You need to get your heart in shape, and then everything will follow. Having a healthy heart is crucial to boosting your metabolism, which in turn burns excess body fat. To excersise your heart you do cardio, or "cardiovascular" (think heart). You need your heart to work at about 80% of it's potential for 20-30 minutes a day. For most people this is as simple as going for a run, a swim, or a bike ride.
Join a football/soccer team or a running club. Get a workout partner to come with you on runs etc. It's easy to cop out on yourself when you aren't feeling like excercise on any given day, but it's harder to say no when your buddy is depending on you, and you on him. Any questions you may have, feel free to ask or PM me.