XML is just something (actually a meta-language) with an HTML-like syntax (pointy brakets, elements and attributes) except it lets you define your own tags.

This is both a blessing, as now you can define what you data IS as opposed to what it looks like, and a curse, because you now have to figure out what it will look like, usually through style sheets or HTML/RTF/whatever conversion.

XML just defines a syntax, no more, you still have to decide what your tags are going to be and how you are going to structure your data. It just offers a standard syntax that XML tools understand, plus the underlying document/data model is a tree, which is quite powerful.

There are tons of Perl modules that can help you process XML, you can find a 6 month old list on XML.com, and note that some of the modules are reviewed in the Module Reviews