Bike New York has a nice page for training for an (imperial) century. Andrew and I took their training numbers in miles, took them as kilometers instead of miles, and converted them to miles.
(For the 8th week, the century distance is not included. As for most big events, the mileage the last week (or so) drops off).
I'm already riding 50+ miles a week (I rode 65 last week). If I actually manage to ride to work each day (for a total of 32 miles), that plus the long ride means I've pretty much met the mileage goal (Andrew is in a very similar situation with his daily commute about a half mile longer than mine).