As a rule of thumb it takes a year to get ready for an Ironman for a beginner triathletes. This is mainly because most Ironman races open for entry about a year before the race and sell out quickly.

Most Ironman training programs work on a 20 week basis so once you've entered you have 5-6 months to work on your base fitness before you start your plan.

In this time learning to train is the most important thing - getting out regularly and learning the discipline that you need. Getting some small races under your belt. Spending time correcting and improving your swim suit and making sure that your wife and family are firmly behind you (swap gender if female).

begginertriathlete.com is a good resource for new triathletes.
BeyondTransition.com - has lots of detail on triathlon races around the world including Ironman races (there are lots of other long course triathlons as well such as Rev3 and Challenge)

Books by Joe Friel and Matt Fitzgerald are good I've used both on a self coached basis for Ironman and I've been happy with them
The Triathlete Training Bible - Joe Friel http://amzn.to/jAXfHq
Triathlete Magazines Essential Week by Week Training Guide - Matt Fitzgerald
http://amzn.to/iFSzSI
Iron Fit - Don Fink http://amzn.to/keXRiP