Thanks for all the info guys. I'll certainly ride the mountains a couple times before the event - just not regularly due the travel time. I think I'll give the century a try. I'm not in great shape, but certainly not in bad shape either. I weigh about 150lbs and may drop another 10lbs just to improve the summer riding season. My bike has a 50/34 compact so I'm betting that I'll be OK on gearing.
I certainly agree with those of you who say a lot of it is mental. I think that is true with a lot of things in life. If you think you're going to fail, well....