HIM Training Time...

I would agree that many HIM plans are only 16-20 weeks long, within the 6 month timeline, but most of those plans don't assume you have little base training before getting into it.

I would make sure you can do the first few weeks of a plan comfortably when it starts.  Almost to the point the first week or two my seem 'easy'.  The plans I used, and have seen, start out with10 -14 hours, easy.  That's a big jump if you can only do 4-6 before that.

Even if you think you can harden up and do the first week, you also have to realize that you will have to maintain that volume or increase it as the plan progresses.

I would suggest finding a plan that starts of pretty easy and builds from there.  Then do some base training  before it starts to get comfortable with the beginning volumes.

while it is probably possible, i would recommend doing some other races first.  i have not done a HIM yet, but will do one or two in 2009.  i decided to do the sprint-oly-HIM-IM progression, because i knew it would take a while for my body to adapt and be able to handle the amount of training it takes to do well at a HIM ('doing well' is very individualized, i mean it as well for me, for my potential). 

what i have noticed in 1.5 years of training, is that it takes a long time to get stronger, more efficient and build up the endurance.  the day in and day out workouts add up over time and i wish i could improve more, more quickly, but fact of the matter is, it takes a while.  also, for me, my thoughts are that i would rather wait, and then be ready when i do the race instead of the whole thing being a sufferfest.