tomoscotto -- just to provide a less smart-alecky response: the advice that I've given to friends who've expressed interest in PBP or randonneuring is to take things one ride at a time. It's always good to have PBP as an overarching goal and four years is a lot of time to prepare, but it's easy to burn out if you go really hard in the first couple of years and lose your enthusiasm by the time 2011 rolls around.
So, yeah, if you want to get into randonneuring, find a 200k brevet and train up to ride that. If you like it, sign up for a 300k. Think about the equipment that you used in a 200k and about what you might want to change for your 300k. Think about how your ate in your 200k and how you felt and whether that should mean changing your diet in the 300k or if you ought to stick with what works. If you like the 300k, sign up for a 400k.
When you complete the 600, then start thinking of a 1200 like PBP. Every ride trains you for the next longest one. Treat the shorter brevets as events in and of themselves and you'll find that each one has lessons that they can teach you.
Enjoy the journey even if your eye is on the destination.