Some resources:

• the Module Reviews section includes information on some XML modules
• the Perl and XML FAQ : http://perl-xml.sourceforge.net/faq/,
• Kip Hampton's articles for XML.com: http://www.xml.com/pub/au/83
• my "Perl and XML" tutorial: http://www.xmltwig.com/tutorial/perl_xml/ now a little old though,

The O'Reilly book is also a good introduction to the subject.