Let me add to Jeanie's question another question:
 
        How do these differ:
 
        1) I went shopping.
        2) I sent John shopping.
        3) I spent the afternoon shopping.
 
        One difference is agency--in 2) the agent of shopping is not
the subject. But how, within traditional or structural grammar, do we
classify the -ing words in each sentence?
        --Bill Murdick