It wasn't a preppy blog so I didn't learn much. (although being a francophile, I still love the blog!)
Lo and behold a lovely gentleman named Ryan left me a comment explaining everything I wanted to know and more. Thank you Ryan. I feel so informed and if you read below, you will too.
French "preppies" are known as BCBG, an acronym for Bon Chic Bon Genre. (Has nothing to do with the store BCBG in the US). They are sometimes from old, aristocratic families, but usually they are haute bourgeois, working in finance, politics, etc...
In Paris, BCBG usually live in the 16th arrondissement, also known as A-N-P, an acronym for Auteuil-Neuilly-Passy. Neuilly sur Seine is a posh suburb just outside of the 16th and Auteuil and Passy are the two neighborhoods that make up the 16th.
http://manstouch.blogspot.com/2009/04/passy-charming-village-in-heart-of.html
BCBG can also be found in the 6th, 7th, 8th and in other posh suburbs and in the city of Versailles.
BCBG love the Dordogne region and often have weekend/country family estates there. Ile de Re is the French Nantucket and is the first choice for BCBG summer home/get away.
http://www.holidays-iledere.co.uk/
BCBG are usually more style/fashion conscious than American preppies, though their clothing choices are always restrained, conservative and classic.
This is the French equivalent of the Official Preppy Handbook: http://www.amazon.com/BCBG-Guide-chic-genre-French/dp/2020091402/ref=sr_1_1?ie=UTF8&s=books&qid=1304024678&sr=8-1
It is a bit outdated, but still very relevant and will give you an idea about BCBG manners, schools, upbringing, clothing, etc...
Here is a spoof on BCBG, about 20 yrs old, but still very funny: http://www.youtube.com/watch?v=8scrJeZECdE
BCBG are generally detested in France and seen as elitist, which is very offensive to French sensibilities. Their manners are mocked and their neighborhoods are deemed passe. (There is a play on words with passe and Passy-get it?)
One other note, currently Lacoste shirts, in France, are only worn by suburban thug boys. It would be VERY un-BCBG to wear Lacoste currently. Kind of like what happened to Tommy Hilfiger in the 90s (though TH was never preppy in the true sense). This is sad, but true.
Enjoy!