here's the Straight Dope: http://www.straightdope.com/columns/001124.html

[I am particularly enamored of this approach: One school of thought holds that all stories can be summed up as Exposition/Rising Action/Climax/Falling Action/Denouement or to simplify it even further, Stuff Happens, although even at this level of generality we seem to have left out Proust.]