The Non-Runner's Marathon Trainer (Paperback)

Now when I've hopefully reinforced your idea, you need a training manual. I had several books at my disposal when I was training, all with slightly different marathon training programs, here's the list (in the order of increasing difficulty of the program)
"The Non-Runner's Marathon Trainer" by David Whitsett
"4 Months to a 4 Hour Marathon" by Dave Kuehls
"Galloway's Book on Running" by Jeff Galloway
"Competitive Runner's Handbook" by Shelly-Lynn Florence Glover

I believe the first two in this list to be good for first-time marathoners. "The Non-Runner's Marathon Trainer" has the easiest program mileage-wise, if you have never run before then this is probably most suitable for you. However, I ended up using the "4 Months" book as the primary source myself for the following reasons.
1) Information was easier to find in "4 Months". It was very convenient to carry around with me and I could QUICKLY find all relevant information while the other books had too much "fluff" in them.
2) "The Non-Runner's Marathon Trainer" emphasizes on every step how their primary goal is not competitiveness but safety and the author discourages you from setting a time goal. If you don't feel competitive at all and just want to finish a marathon, it's perfectly fine and "Non-Runner's" is a great book for you. However, I have always been a competitive person in my life, so "4 Months" suited me better.
3) The weekly long runs in "Non-Runner's" go up to 18 miles. Now this lets you finish the marathon but I feel that a longer run would be better for two reasons.
First, the harder you train, the easier the marathon itself is. My personal training program was relatively hard and it required great effort to complete it. However, running the marathon itself was really surprisingly easy and I could handily beat the four hour mark. There's nothing wrong with an easier training program but I promise you that the more you've trained, the more you will enjoy the race.
Second, many scientists believe that human body is capable of doing whatever it has done before plus about 10%. "4 Months" follows this idea and the longest run there is 24 miles. At the same time "Non-Runner's" has 18 miles as the longest run and then focuses on "beating the wall" i.e. a point of exhaustion that you're supposed to hit at around 20 miles (notice how this is approximately 10% more than 18). My longest run was 24 miles and there was no wall when I raced! Your own experience may vary but longer runs do help you greatly.

These are the reasons why I'm giving "Non-Runner's" just 4 stars. Now don't get me wrong, it's a great book and it does help you run a marathon (which is the greatest thing you'll ever do!) but I feel that for some people other books would be more suitable.

Anyway, whichever book you get, good luck with your first marathon!!