There are so many good training programs out there, but the coaching approach I am personally most fond of is running great Jeff Galloway's. I like Jeff's approach because it is reasonable and doesn't assume that you have nothing other than running to do in your life.
You said that you used to be a sprinter, so I assume that you have not really run a lot of distance. Galloway's program increases your mileage slowly and emphasizes the long run only once a week. In fact, he recommends that you actually may want to reduce your current weekly mileage and emphasize your long run!
The main components of Galloway's Marathon Training Program are:
1) Keep the daily mileage you have been running (and in some cases decrease your weekly mileage)
2) Increase the weekly long run 1-2 miles every 14 days. This applies to runners of all abilities.
3) Build to 26-28 miles before attempting the marathon. Do this last long run 2-3 weeks before the marathon.
4) Run slowly, take walking breaks and enjoy each run.
KEY CONCEPT: Increase your total mileage by lengthening the long run, not by acumulation of daily increases.
Jeff published a book some years ago called Galloway's Book on Running. My own copy is dog-eared from years of use. You may want to pick this classic up. In it you'll find tons of information on marathon training and weekly workout plans broken down by your race goal pace. I highly recommend it. There's also a newer one called Marathon You Can Do It!, which I haven't read, but I'll bet it's great.
Happy training! Hawaii is awesome!
Little known fact about Jeff Galloway: He founded the chain of running stores called Phiddipides...there is one located in the San Fernando Valley on Ventura Boulevard in Encino...check it out!