Or the other way round!
If you get the Eurostar into Paris it can get a little tricky to find your way around. The Eurostar arrives into Gare Du Nord. On leaving the train head to the end of the platform and you will find yourself in a very large concourse area. Turn left and walk to the far corner. You will soon see signs leading downstairs to the RER and Metro (and a huge shopping centre too)
Keep walking straight ahead and you will come to the ticket office.
The best way to get from here to Disney is to take the Réseau Express Régional or RER trains.
Paris public rail transport is split into 3 types, big cross country trains TGV, smaller regional trains RER and the underground Metro.
Metro lines are numbered and RER are identified by a coloured letter. Disney is at the Eastern end of RER A, the red line which runs across Paris. The station at DLP is correctly known as Marne-La-Vallee Chessy.
Gare Du Nord is on a big inter change of many RER and Metro Lines but it is all well sign posted. Take RER B (blue) or D (green) to Chatelet des Halles and change onto the RER A.
It is very straightforward but can be a faff with cases etc.