I published a book through a print-on-demand outfit. They have
defrauded me by giving no figure for sales by Amazon.com while many of
my friends have bought the book from Amazon. How can I get Amazon.com
to give me the number of copies they have sold in the last quarter of
2003?

Do you have a contract with Amazon?  

If you do have a contract, what are the contract terms relating to
Amazon providing you with sales information?

If you are not affiliated with a major publisher, they may try to
muscle you around and not provide you with the sales information
similar to the way the print-on-demand outfit did.

You should call around the Amazon offices and get bounced from person
to person until you find someone that can pull together the sales
data.