Just one piece of advice Norma - start the training before you hear whether you've been accepted or not.
Regarding marathons to go for if you don't get in - from memory there's Paris, Sheffied, and the Robin Hood marathon all round about the same time, so it wouldn't mess up the training schedule much if you had to switch.
There's also the possibility of getting in via a golden bond place.
Regarding training, I think the main aim is to gradually build up the mileage/time on your feet. If you can run for an hour at 9 min miles, that's just over a 10k. The first time I did it I was aiming for a half marathon by the end of the year, which worked pretty well, so see if you can find a few 8 and 10 mile races to do over the next couple of months, and then look toward the half by around Xmas. There are plenty of online schedules around (try searching for Hal Higdon or Bruce Tulloch, or elsewhere on this site), or ask in the training section. If you start training now, you've got plenty of time :o)
Iain