What is the best way to go about this??? I would like to take a train for the majority since it is faster. I just don;t know what city to go to from Paris, and then how to get from that city to Mt St Michael. I am leaving in a week. Please help, thank you!
There's a train from G. Montparnasse to Pontorson that takes about three and a half hours. From there, it's about five miles to MSN, and there are buses (they might be seasonal). Toss in the notiional half hour to get from somewhere else in the city to Montparnasse and you're looking at four and a half hours. You can drive it in a bit less than four. Plus, you're free to head back when you're done. I don't think the trains are very frequent in either direction.
Definitely drive. By the time you get close to MSM, you're in the middle of nowhere and I wouldn't want to rely on public transportation.
The fastest way (3 1/2 - 4 hours) from Paris to Mont St-Michel is to take a TGV from Paris to either Rennes or Dol de Bretagne and a highway bus operated by SNCF (French National Rail) from there right to Mont St-Michel. For complete timetables go to the German Rail site.
If you stick with public transportation, I like Tim's idea best, especially the Dol routing since it can give you a twofer. The dol/menhir itself is on the south side of the town (maybe a twenty-five buck taxi ride/wait/ride) and would take a bit less than an hour.
Get a car in the morning from the neighborhood, have the GPS tuned in and head out. I think that is the easiest; if you spend the night out you can really see a lot on your drive. We spent about 2-2.5 hours @ MSM.
@Liz (the OP): In researching this and when you get to France, it may help to use the name Mont Saint-Michel or Mont St-Michel (the hyphen isn't a biggie but Michel might be).