How do you start serious training?

I will be taking part in my first 5k on Oct 3rd. I will be walking, but hey I only had surgery june 18th and I am down 102lbs so I am ok with my progress. But what I would like to do is to start to build toward a 1/2 marathon and half ironman. I started out at 405 pounds and I am now 303 so I am about 50 pounds short of really being able to run/jog. I have an iphone and the nike chip to take my walking now, but how do I start to actuallt develop a training routine? I get a lot of inspiration from this site and the one thing I see very clearly is that the people that  develop a passion in fitness have the greatest succuss. Any and all pointers will be be gladly taken.

Welcome and congratulations on your weight loss. It is a great feeling. My heaviest weight was 470. I started the couch to 5K walk/jog program found at coolrunning.com. That program started it for me and now I can run over 8 miles easily and qill run in the Rock and Roll San Antonio 1/2 Marathon November 15 and the Chevron Houston Marathon January 17. The thing that got me to really pick up my trining was when I actually signed up and sent in the check for my 1st triathlon. So my suggetion is to start with a walk/jog program like couch to 5K then sign up for a race. There is a feeling of commiment that I had which got me to train even on days when I didn't want to at first. That feeling of commitment changed to an awesome feeling of accomplishment as my fitness level increased and I completed my 1st Triathlon. Posting my workouts on here also helped me to be accountable to completing them. I haven't done as good posting them the last few weeks because of work, but hopefully I will pick it up. Keep up the great work and get out there and Dare Greatly!

First of all, you're doing excellent already with your weight loss.  Having monitors like the Nike Chip is great and allows for a trackable monitor of progress into fair units of 30-45 minutes.  You may want to think about getting a chest strap also to make sure you are not working out your heart too hardcore.  Although you may think pushing yourself to the limit is the best, it actually would help to stay in the cardiac range.  I find myself pushing too hard and getting out of cardiovascular exercise and more into non-aerobic exercise (i.e. your oxygen-CO2 transfer cannot keep up with your muscle demands).

You have already started.  Just stay with and keep pushing to improve a litte at a time.  As the weight drops, the walks will include some jogging, the jogging will replace more of the walking, the jogging will get faster and the walk breaks will bevome slower jog breaks. The distance will increase some from week to week.  As you get bored you will need different routes and venues, 5 Ks become 8 and 10Ks.  10K become half marathons athen full marathons. Halves and full marathons become dual and tris; jogging can work into crosstraining and/or brick workouts with biking, swimming, or whatever gets the juices flowing for you, they are all good things.
Just don't try to do it all in one day.  Set your Pesonal Record (PR) to be better than your previous achievement and keep working it by the week and month.  Race results to race results.  Over doing will actually cause you a setback.  SO be smart and just be persistant and consistent. 
It took God 6 days to create the world then even he took a day of rest.

You are in dude. I look forward to your accomplishments and we do want to read about them right here on this Exercise and Fitness board.  There are lotsa folks in the same point of the journey as you and need your inspirations and example.