A number of web sites and articles have discussed SOAP, although I haven't seen very many examples of programs that demonstrate how to use them. A good starting point is Dave Winer's site at http://soap.weblogs.com/. This includes pointers to the SOAP specification, as well as a running web log describing the state of SOAP affairs.
The SOAP specification, which is published (and endorsed) by the World Wide Web Consortium, is available on-line at http://www.w3.org/TR/SOAP/.
The SOAP::Lite module is available at http://www.soaplite.com/ as well as via CPAN. Paul Kulchenko, the author of SOAP::Lite, has worked hard to improve this module and gave me invaluable debugging assistance when working on this article.