Premex,
I purchased my Paris visite pass at my hotel the Hilton CDG airport located at the CDG airport. I believe you can also buy them at the train station at the CDG airport. It costs 100FF and was good for unlimited travel metro/bus for a whole day. Remember to copy the pass number onto your Metro ticket....
I bought one for each day that I was there because I didn't know how much it would cost coming for the outer zones into Paris each day. It was easier that way...
Enjoy!