PL- a 'get you round' might look something like:
Swim 2 hours
Bike 8 hours (112/8=14 mph average)
Run 6 hours
Adding in transitions then that'll get you a 16:xx something.
I think you're possibly getting a bit ahead of yourself in the worry stakes. If I'd told you that you had to run a marathon after only a few weeks of running you'd have said no (I guess), so trying to judge whether you are capable of covering 112 miles at 14mph at this stage is too early. Ditto with the swimming. The more you do the better you will get.
That said, the IMW bike course is an absolute b*****d. If you do want specifically do IMW in preference to any other iron distance you will need to find lots of hills to practice on.
Edit: x-post with Seren, but relieved we didn't flat contradict each other
Edited: 06/07/2012 at 14:23