Start out doing what you feel comfortable with. If all you want to do is walk then walk and just push yourself a little bit more each time. Even if it's "just walking" it's a heck of a lot more than "just sitting". Right? In my situation, I started off by walking and then would add in some jogging until I was running. You should check out the exercise forums and also you might be interested in the C25K program. It gets you from sedentary to running at a comfortable pace. You will find that your body tells you when to advance and when to try new things
