difference for dummies: Nouveau is soft, flowing, Decó is sharp, static.

i wouldn´t say neither Eiffel Tower nor Klimt's paintings belongs to Art Noveau movement....The first has no-style, is an engineer construction; Gustav Klimt, Otto Wagner, Victor HOrta, ...they belong to Viennese Secession, wich is not the same that Art nouveau.
and i agree with Mr Trilby too.