Bike New York has a nice page for training for a century in 8 weeks. Basically base miles and a weekly long ride.
I modified the plan successfully for a metric century last year.
The other piece of advice I have is make sure you train on terrain that is as difficult or harder than the actual course. You'd be in for an unpleasant experience if you train in a flat area and ride a hilly century.
Cheers,
Charles