I'd like to comment that you shouldn't go overboard with running right away, particularly since you are just starting to workout for the first time in awhile. Walking is excellent for your body as well (better in fact, if you are moving the same distances... i.e. a 3 mile walk is better than a 3 mile run, but as stated above obviously a 20 min run is FAR better than a 20 min walk since you can burn more calories faster) and 3 miles per day is a very good start. Keep up the walking and slowly work your way into running. Attempting to do too much running too quickly can result in a number of problems that you don't need.
As you feel yourself and your legs getting a little stronger pick up the running more a little bit at a time and you'll find the pounds falling off before you know it. Keep in mind that a healthy diet is as important (if not more important) than exercise alone. You should be keeping an eye on your portion sizes as well as the quality of the food you are eating. Find healthy foods you enjoy and work them into every meal.
Good luck with everything, getting yourself started and developing good habits is the first and most difficult step of getting back into shape. Once you are able to develop healthy habits the rest of it will come easily and turn out to be very enjoyable.