def use the metro and the rer
metro is underground fast bus on tracks basically, comes every 5 mins and is bombing fast at starting + stopping! and cheap too like €4 ish for that journey i'd guess.. its def the best way to travel around paris, the roads are a NIGHTMARE
rer is a train service that meets at a lot of the metro stations so its for the longer journeys (disney land paris + airport)
it'll take you about 2 mins to work out how it all works
http://www.kigoobe.com/parishotel/img/carte.gif
look at that link the letters represent the RER train, and the numbers represent the metro service.
all the lines run both ways, and each 'dot' represents a stop, if there's multiples lines at one dot or junction then thats where you can jump onto another line (using the same ticket)
which part are you going to?
was there for 3 days in the summer with the mrs, really had a cool time
seriously tho, roads are a no go..