Lots of good advice above, so I won't repeat what has already been said. I will say, however, that it's recommended that you have a good running base for at least 2-4 months before you start training for a marathon. The number that is thrown around and considered a "good base" is 20 miles/week. Marathons aren't going anywhere so you have time to properly build a base and train without injury or burn out.

In addition to the above Hal Higdon books/links, I also like The Runner's Handbook : The Bestselling Classic Fitness Guide for Beginning and Intermediate Runners (2nd rev Edition) and The Competitive Runner's Handbook: The Bestselling Guide to Running 5Ks through Marathons both by Bob Glover and Shelly-Lynn Florence Glover.

You may want to work yourself up to the distance. Do some 5K, 8K, 10K, 15K, etc so that your joints/muscles, etc gradually become accustomed to the stress of running.

Good luck !