StetsonUK - v'course you can go from couch to 26.2 in 1 year; but it'll take all of that year in effort. the biggest risk is doing too much too soon and getting injured.
add a bit of strength work to the running (gym stuff and core strength training) and that should keep the knee twinge at bay and keep you on the roads.
the RW schedules are good but don't stretch to more than 3-4 months so get yourself a copy of Advanced Marathoning by Pfitzinger & Douglas - don't be scared by the title! The best bits in it are the long term schedules which are quite bendable to an individual's requirements
i started running for the vain cause of shifting some beer weight. after a few months of treadmill plodding i realised that running was the highlight of my gym trip so took it outdoors - outdoors in aberdeen, i might add!
after 8 years, what i love about it now is the pure honesty of the sport. with work, anyone will get to the top of their potential and deserve it.
my first race was the 1999 BUPA 10km at balmoral and i was chuffed to finish and in 52mins. then came some GNRs and i got a half mara time of 1:45. from then, i dug in to do a full marathon and in 2006 got my ultimate goal of a sub 3:00.
apart from reminiscing, what i want to convey is that i found something i love doing, that gives me confidence, discipline, a fair bit of ego boosting but mainly a refuge and a means of grounding. whenever i feel crap, the old me would go to the pub - now i go for a run and feel 100xbetter every time. that outlet will always be there even if the times stop improving.