Getting from Charles de Gaulle Airport to Versailles

Half of the answer is:

From CDG take the RER B to Notre Dame - St Michel. At that point, switch to the RER C (Direction Versailles - Rive Droit) and get off when you arrive.

This has gotten you to within about a mile of the hotel. I can't picture a taxi rank at the station. There's a bus stop, but I don't know how the routes work (There's usually a diagram either right at the stop or in the shelter).

Taking the RER is your fastest and cheapest option, but I need to correct what Ed wrote. The RER C goes to Versailles-Rive Gauche (the station closest to the chateau), not Versailles-Rive Droite. Be aware that the RER C divides on the west side of Paris so be sure to get on a train going to Versailles Rive-Gauche. The nameplate on the engine will be VICK.

Take a taxi from Versailles-Rive Gauche to your hotel.

Tim's correct, I don't know my left foot from my right. There's probably not even a Rive Droit station anywhere near Versailles. My recollection of taxi stands and the bus stop remains as stated; I was, in fact, picturing the station that Tim stated correctly.

Ed,

Your memory is better than you think it is! There is a Versailles-Rive Droite station and it is actually a little closer to the hotel than is the Versailles-Rive Gauche station. It is served by SNCF trains out of Gare Saint-Lazare. However, those trains take a roundabout route so it's faster to take the RER C to Versailles-Rive Gauche.

For the record, I'm only guessing that there is a taxi rank at Versailles-Rive Gauche. Since it's the closest station to the chateau, I would think there would be a demand for taxis by people who want to visit the chateau but don't want to take the RER to get there