The cruise terminal in New Orleans is right next to the Riverwalk Mall. I would not consider the French Quarter to be with walking distance though, unless you like very LONG walks! There is a trolley we locals call the "Lady in Red" that runs from the Riverwalk to the French Quarter and is an excellent way to travel along the River. Besides the Riverwalk Mall, it also makes stops at Spanish Plaza, the Aquarium, and Jackson Square. I hope this helps you out.
Yuyi64, if you are a local then you would know that the French Quarter is certainly within walking distance from the cruise terminal! I used to live in New Orleans and I would walk everyday from Poydras St to the St Louis Cathedral, read for 1/2 hour and walk back.
The aquarium, Jackson Square and the French Quarter/French Market is definately within walking distance. Just make sure that you have some good walking shoes on.