Over on PHPEverywhere this morning, they have a PDF file that's an excerpt from the book PHP Programming for Windows. The sample chapter focuses on using PHP (on Windows, obviously) to program web services, and it not only talks about how web services are created, but how you can narrow it down and just use PHP to create some pretty cool applications.

This chapter talks about things like SOAP (how to use it and some sample code), WDSL (web services description language), and UDDI (uniform description, discovery, and Integration). They show you how to get it all set up and working with various severs and all for your Windows machine, and how to use some of the client software that comes with them (like the SOAP Trace utility) to help you figure out exactly what information you're passing back and forth.