Thanks very much, both of you!
I'm fortunate to have a pretty decent bike that fits me very well. I'm thinking about putting some drops on it (came with flat bars); it should be a fair machine for doing just about anything but road racing or serious off-road downhillery
I'll check out the century training threads, and also "The Complete Book of Long Distance Cycling." I also like the suggestions on Ultracycle's century nutrition page -- both sounds kind of like what I'm eating already, and sounds like good science.
Thanks again!