Paris by Train

Thinking about how to get from the airport to the apartment on Rue St. Paul, I came across this site, Paris by Train which gives the directions from the airport to Paris, although it was posted in 2008.
The RATP ParisVisite page recommends the RoissyBus ("RoissyBus is the most direct and easiest mean of transportation from Charles-de-Gaulle Airport to the center of Paris.")
The RER train takes the same and looks more straightforward. Take the RER to Chatelet-Les Halles and then the #7 Pink metro line to Pont Marie (Cite des Arts). More info at Aeroports de Paris.

I also downloaded the iphone app from RATP, which allows you to search for a route from one station (bus, RER, Metro) to another, which you can also do on the RATP website. We just have to remember that our metro stations are Pont Marie on the #7 Pink line and Saint Paul on the #1 yellow line. And, oh my god, the RATP gives you your carbon emissions for the trip: Les émissions de CO2 pour cet itinéraire sont estimées à... And we can remember that there are also many buses that stop at "Saint Paul": BAL, N11, N16, 69, 76 (which you take east to the Pere Lachaise cemetery, and 96. They offer a map of Paris with the bus routes which I wish I could print out (but maybe they offer it in print form?).