It does depend on which airline you arrive. If it arrives at CDG1 (United and TWA), you must get a shuttle bus to the train station which will take you into Paris and you can connect directly on to the Metro. CDG2 is exactly as other correspondants have told you. You should have little problem, check out www.tf1.fr which should advise yous of there are any strikes which occur in France all too regulalry. By the way, Eurostar is going to be hit with strikes in the run-up to Christmas the news here warns us