When's the last time you ran?
Running can get you insured fast. Over-use injuries are your enemy when starting from scratch. 17 pounds extra at your height will take a toll as well. You definitely want to lose a few while you are training.
My advice is also not to target a certain time. This year is participation, next year is a time goal. It is an annual event for Pete's sake.
I would start the running program gradually. Ideally you only walk 80% and run 20% of your workouts in the beginning and limit it to a short distance like a mile. ALWAYS take at least 1 day rest between runs. If anything starts feeling funny or sore, put ice after the workout and take a longer break until there is no pain. Don't run through injuries.
Join us on this thread. Lots of exercise and weight loss discussion. You can set a target for the end of the year, so you don't fall off the wagon after the tirathlon:
http://forums.pelicanparts.com/off-topic-discussions/726649-ppot-weight-loss-fitness-challenge-2013-a.html
Good Luck,
George