Couch to 5K program (C25K).
It worked for me (mind you, I was 40 lbs heavier at the time) and I highly recommend it, and it sure beats the elliptical for cardio. Tips:
Be nice to your feet -- get a good pair of running shoes. They don't have to be expensive at this point, but designed for running.
You don't need an expensive Garmin but you'll probably want at least a cheap sports watch.
Pick out a race when you start the program and register early. That's an incentive to complete it. When picking out a race, pick a midsize one, so you won't get lost in the crowd or be one of so few that there actually is a risk of finishing last. Also, pick one that says "run/walk" so there's no way you will finish last. And always go for the ones that give you technical or tek or tech shirts instead of the normal cotton ones, they're way better. (continued)
Look at the race course. If there are hills, practice running hills. If not don't worry about them.
Even though the program is 8 weeks, pick a race 10-12 weeks out. That way you won't have to worry about repeating weeks if you have to.
Go slow. If you're alternating between the treadmill and the road, slow down on the road even if you think the pace is comfortable. Your legs will carry you faster on the road and you'll wear out quicker. If you do most of your training on the treadmill at least get out on the road once or twice before the race.
Stick to the program. At one point you'll probably think "hey I'm feeling really awesome I'm going to run 3 minutes instead of two". It sounds crazy, but resist! At this stage it's really easy to overtrain and wear yourself down.
And have fun!
A word of caution, my first 5K was in July. Seven months later I'm getting my Garmin, heart rate monitor and Gu together to run 10 miles with my marathon training group. 3.1 miles used to seem impossible. Last week, my recovery run was four miles, and there was nothing to it!