With what you're doing already I don't think you'd have any problem
completing a century. If you ever want to do a self-supported one to just prove it to yourself, I'd be more than happy to join you. Unhookt is right about the hills though. I don't hit them nearly enough myself and the Sierra Century is going to kick my arse if I don't practice em' more.
You live in Natomas right? We could ride from there out toward Berryessa and turn around at 50.0 or make a loop. Just a thought.
And you might want to think about joining a cycling club. The Wheelmen have long rides about every day of the week.
http://www.sacwheelmen.org/08mar.htm . Just make sure you're going to a flexible and not a training ride.
