Hi Val,
Well done on committing, its a real challenge and not something I can do yet. My SO is running a Marathon in October and she is about halfway through her training schedule. Needless to say I hear quite a lot about her plans and training tactics and I even partake in some of the runs. She is following the training guide by a man called Hal Higdon:
http://www.halhigdon.com/
Which is really fairly simple, it comprises three components:
1) The Long Slow Distances (LSDs), once a week, starting low and building up to several 22mile runs (up to 1m30s per min mile slower than race pace).
2) Pace runs (at marathon pace), mostly 6-11miles as you progress.
3) Cross training, short 3-10mile runs once or twice a week with another session of tennis/swimming/squash/etc.
She is now on 40 mile weeks and is aiming for a sub-4 hour marathon, which I'm sure she'll make.
Anyway, best of luck mate and let us know how you're getting on!