Hi Siobhan,
There were many is the same boat for 2008. I have also signed up for 2009.
I did 2008 for similar reasons to you - if you really want to bore yourself you can read my trials and tribulations on my blog :)
Google Hal Higdon, a Marathon trainer/runner in the US. Many runners work to his training program. Personally, the first thing for me when I started this year was to get into a routine of exercising. So if it's say, 1 a week, 2 a weekend, just get into the routine for the first couple of months, ensuring you make the time to exercise. As you've never done running, start with walking, then fast walking, then you might want to intermittently run e.g. walk for 5 mins, run for 2 mins, then build up gradually to aim for 5 mins walk, 5 mins run etc.
It really is possible, so don't be scared. You have a whole year to worry othewise, and you have plenty of time just now.
I also joined a gym to help me, just for the year, but will be unable to continue it I expect when it expires in February. However, it really helped me be less conscious of what I was doing, with some guidance from trainers there.
To be honest, I'm still a jogger and not a runner. But did complete it.. yes yes.. to whoever reads this.. the videos showed me in near state of collapse at the end with heaving. But my god I did it! You can too Siobhan.. really. Start slowly and build up. You have time.
Best of luck,
Tracy