In reply to Richard Carter:
I did my 1st "25" a few weeks ago. Great day and got 1hr2m55s in windy conditions which i'm happy with. Here's how my buildup went....
Bought a regular road bike about 6 months and have been doing anything between 90 & 200 miles a week.
Started doing spin classes as you NEVER put in as much on a stationary bike as you do in a class environment.
Started spending more time on the drops of my road bike to get used to the more aero positon (having spent 95% of my time on the brake hoods).
Long rides out (100mile plus ones) to get some base fitness in.
Also started using my shorter rides as interval training - working as hard as my legs/lungs would take me up certain hills.
Got a Garmin Edge with HR and started understanding what level I could maintain my heart rate at without blowing over "X" time.
THEN
I borrowed a TT bike from my dad (never used it before until the day before the race)
Borrowed a skin suit and aero helmet
THEN... The race
Set off too hard, went through a whole load of panic when i'd passed someone after 5 mins and thought i'd gone out too fast, backed off a little for a short time then hurt myself for the remaining time knowing that I either had it in my legs OR i'd blow BIG time... Only started flagging in the final 2 miles - but then it'd just a "grit your teeth moment!".
Finished 24th from over 100 registered.
If I were you i'd just get the miles in over winter on your existing bike then borrow/lend/hire one the week before.
I'm so excited to do some more next year now - the magical sub-hour is the aim!
Good luck.