I think that "ZX" if for USA sales, and "MZ" is for international sales. If the number is the same, it's the same camera. The only difference would be in the warranty.
As far as ZX-60 vs N-55 I don't know the specifics of the cameras, but they are both fairly entry level AF 35mm SLRs. In build quality or image quality they are basically identical. You should look at the list of features for each model, and see if one has something you want that the other doesn't.