RER or metro to gare de Lyon/to cdg from gare de Lyon

There's four or five that are about equidistant. Three (St Michel, Odeon, and St Germain) are all on Line 4. Use one of them and go northbound to the Chatelet / Les Halles (metro side) and switch to Line 14 to G. Lyon. You're looking at only ten or fifteen minutes for the whole deal. It'll take a standard metro ticket. For the second question, if CDC means the CDG airport at Roissy, take the RER A to westbound Chatelet / Les Halles (rer side) and switch to the RER B northbound to go to the airport. It'll take the better part of an hour to get out there and you have to buy a special ticket which will stiff you ten or twelve bucks. Note: two RER B trains share the same platform and the line splits up around Aulnay - - make sure you get the one going to the airport and not the one to Mitry-Claye.

An alternate route from rue Dauphine to Gare de Lyon would be to walk across two bridges on the Seine to the Pont Neuf metro station, take metro line 7 one stop to Chatelet, and metro line 14 from there to Gare de Lyon.