The home page for Amazon Web Services (AWS) is www.amazon.com/gp/browse.html?node=3435361 [1]. From that page, you can register for an ID, download and read documentation (including code examples in a variety of languages), and participate in forums for AWS developers. A frequently updated Weblog with news and ideas about AWS is at aws.typepad.com [2].
All of Amazon's Web services can be accessed using either SOAP or REST. An overall introduction to SOAP, including XML examples, is at www.intertwingly.net/stories/2002/03/16/aGentleIntroductionToSoap.html [3].
For more information about XML-RPC, which preceded SOAP and is a simpler protocol, go to www.xmlrpc.com [4]. Libraries for XML-RPC are available for all popular languages.
Links:
[1] http://www.amazon.com/gp/browse.html?node=3435361
[2] http://aws.typepad.com
[3] http://www.intertwingly.net/stories/2002/03/16/aGentleIntroductionToSoap.html
[4] http://www.xmlrpc.com