New on the Ibuildings techPortal today is an article from Michael looking at XML transformation with PHP and XSL (XML-based "style sheets").
If you want to transform XML from one format to another, and especially if either the input or output XML is complicated or the transformation itself is difficult or awkward to express, then XSL may be a good choice. XSL is the eXtensible Stylesheet Language; a family of three W3C recommendations to do with the transformation and presentation of XML documents. This article will walk through some examples of how XSL and PHP can be used to achieve these types of XML tranformations.
He starts off by describing what XSL looks like and how it relates back to the XML you're applying it to. XSL allows you to take an XML file and work with it as a data source to pull bits of information out of or modify and push back out the other side. He gives three specific examples: pulling information out of an XML file, rewriting URLs and one of the more handy things PHP allows you to do - directly call PHP script inside the XSL document for those things that the normal XSL standards don't include.