The 10 ticket book (carnet) is only for travel in the city centre. To get to Disney you need to either buy single tickets from the counter (tell them your destination is Marne-la-Vallee) or you can buy a day ticket (mobilis 1-5) which normally works out cheaper.
To get to Disney is pretty simple. I believe the Marriot is near Glacière metro station. Walk to this station and then take Metro line 6 to Nation. At Nation you need to switch to RER line A to Marne-la-Vallee. This is easy to do, just follow the signs of an orange A in a circle. Not all trains on RER line A stop at Disney. When on the platform at Nation, you'll notice a large board above your head with lots of place names on it. Next to some names there will be a light. One of the last names will say Marne-la-vallee. Make sure that the light next to it is turned on when you board the train. If it's not, that train wont stop at Disney.
The train station at Disney is located next to the park gates. Make sure you keep your train tickets handy as you need them to get out of the station.
