How does one go from Charles de Gaulle airport to Gare du Norde?
Ride the RER B. Piece of cake. Just watch for signs as you come out of the arrival hall and you'll have no trouble. PA system announces upcoming stops and you can see stop names through the windows as you pull into each station. Also line diagrams are in almost all the cars.
Follow Ed's advice. The current fare is 8.50 EUR. For detailed instructions, including photos, see the Paris by Train site.
Ask at the information booth at the airport. Very easy.
You can purchase the ticket at one of the machines and unlike Rome, it does not need to be validated. It will get scanned as you go through the gate. If you need to get to another destination via the Metro or RER, the same ticket from the airport will get you there so long as you don't exit the station. Just follow the signs. Bon Voyage.
I just want to clarify when I said the same ticket will get you to 'another destination', I meant another stop within the boundary of the Metro map. I did want people to think they can get to Chartres or Versailles on the same ticket.
I printed a copy of the metro map and it was very handy.
George,
As the others have mentioned, that's a really easy trip via RER 'B'. You may want to have a look at parisbytrain.com for a pictorial instruction on the route to take. The route shown on the website seems to look a bit different when one is actually walking it, but it's accurate.
Note that there are two ticket offices at CDG. One deals with TGV only and the other is the one you'll need. If there are huge queue's, you can also buy tickets from the automated Kiosks. However, these ONLY accept the newer "chip & PIN" credit cards, as well as Euro cash.
Are you staying in the vicinity of Gare du Nord or transferring to another train or Metro there?
Happy travels!