KnightRT has the right idea. HIIT style workouts really boost my endurance.
I was half joking about the biking clothing, but the serious bike rider will go more out getting the padded shorts, the gel seat with the crotch hole, the shoes that lock onto the pedals, etc...
Ignore anyone who tells you to quit lifting weights, and anyone who advises you to quit brushing your teeth. I believe that adding some muscle can improve biking performance.
My brother in law is a bike-riding maniac, who has done some ridiculous amounts of biking, and when I hit the trails with him I usually don't have a problem keeping up. Then again we usually are just casually riding, and not racing. I actually take it a little more intensely by myself.
I would say spend the winter working on building. Toward the end of winter focus on leaning up, (like everyone else,) which will lighten you for riding. Once you can start riding, do KnightRT's workout, and also focus on riding some treacherous hills to prepare for the summer.
Tribex has been tested on bike riders, and has shown better recovery and reduced cortisol levels. Also taking Surge post riding might help, and will kick Gatorades ass.
During the riding season I would think doing an EDT workout twice a week just to prevent muscle loss would be beneficial, and might not get in the way of you biking if timed right. (After the first week of being unable to move from EDT that is.) All you would want to do is work out enough to prevent, or slow down any muscle loss.
Oh yeah, spend some of the winter doing the 100 reps to bigger muscles routine for legs. Also you might want to check out Waterbury's Endurance-Training Guidelines here:
It also has a link to the 100 rep program, as well as to his Outlaw Strength and Conditioning (OSC) program.