You can take the organised tour bus that leaves from Hotel New York, although most of the time is spent in the bus. Or you can take the independent route of the RER train station; which is beside the park and shuttle bus station, and in 30 plus minutes you'll be at Paris
I went to paris on the RER. Its easy to use and the trains run often. You can also see the parts of paris which you want to see. The Infomation office outside the station is really good at given advice on getting around and they also sell maps and guide books.
I would also vote for the RER. We've done DLP as a day-trip from Paris and the RER is about 30-45 minutes (depending on where in Paris you're going) and the trains typically run every 10-20 minutes from 6:00 to 1:00. Very easy.
Does the price of the ticket include running around Paris on the Metro or is that a separate ticket? If it is separate, can I buy it at the same time I buy the train ticket or do I have to wait until I actually get into Paris and buy it at a metro station?