Charles de Gaulle is a major international hub, so you shouldn't have any trouble finding a flight, regardless of where you're flying. There are six major train stations in Paris, each of which handles traffic to different parts of France and the rest of Europe. TGV services also link Paris with Amsterdam and Brussels.
Euroline buses run from Paris to cities all over Europe.
There are also ferries and hovercraft between Ireland and France. There are dozens of ways to get to and from Paris' airports, from rapidfire shuttle trains to the standard assortment of pokey public buses, private shuttles and taxis. There's even a bus that runs solely between the two airports. Say what you will about driving around Paris, but the city's public transportation is world class. No matter where you are, chances are there's a metro station within a few blocks.