I did it last year, my first time ever. You can do it! What worked for me: Following the suggested mileage schedule provided by the Cascade Bicycle Club. I followed it pretty diligently, and had no trouble (relatively) on the ride itself. Also their training suggestions PDF is helpful. Keep reminding yourself that it's not about how fast you do it; it's about finishing it and enjoying yourself.

I'm planning on doing it again this year, so I'd totally be game for keeping track of STP training here somewhere -- let me know if it happens. And if anybody here in MA wants to do long training rides, I'll be looking for biking buddies! (I trained alone last year; it was very lonely.)