I am a newbie myself, although I have logged one marathon. I am sure that just about everyone on here can give you more tried and true advice, but what I did worked for me. I was also pretty new to running when I decided to run a marathon and was only running 15-20 miles a week when I started a 3 day a week program. I cross-trained a lot, but I met my goal and I felt prepared. I was intimidated by all of the articles and posts that recommended a much stronger base and a much more running-intensive training, but I stuck to my plan and it worked. Anyway, just my two cents and good luck and have fun!