You can see the 'training' I did at http://mactually.co.uk/ - there are monthly mileage counts on the right hand side toward the bottom of the page.
I did 200 miles a month in each of the three months leading up to the K100. Much of this was my 5 or 6 mile a day commute, with some bigger rides thrown in on weekends. The biggest ride I did in the run up was 90 miles on the road (but on the MTB I was planning to ride).
I finished. Last. In the dark. Broken. But I finished. To be honest, I completely blew on the ride over the border to Newcastleton and did the last half on bloody mindedness.
Me, last, in the dark and broken:
My plan for this year is: ride more over the summer; get a kick ass bike; drink beetroot juice; finish again, but hopefully not last and a bit less broken than last year*.
If I can do it, you can.
*The cut-offs are going to be tighter this year, I believe. I'd not have made tighter cut-offs last year, only leaving the last one 15 minutes before it closed.
(Ralph, am I still okay for a lift?)