Cityrama have organised trips through Disney that leave from the Hotel New York.
Note that if you are using DVC points for DLP you have to purchase length of stay park passes. This would mean that you trip to Paris would effectively waste a park day. That said Paris is beautiful and can understand why you would want to wish while here
They do offer an evening trip from the Hotel New York which leaves at 9pm. This would mean that you could spend some time in Paris without wasting any precious park time.
Its also very easy to catch the train int paris and then tour it by yourself, if a guided tour isn't quite your thing.
The train station in right in the centre of disney resort and the trains only take 30 minutes or so.
The European Capitals cruise looks amazing! We were quite dissapointed we have holiday plans for 2010! Plus I want my first DCL experience to take in castaway cay!
Definitely recommend taking the train into Paris direct from the station at Disney. It is quite easy to navigate on your own as most signs are in English as well as French. The train is also a convenient way to do some shopping as the first stop down from Disney is a large modern mall with a supermarket.