In addition to what others have mentioned, you may also wish to look at XML::LibXML and XML::LibXSLT, which are very fast, modern, GNOME c based modules that are very powerful.

Kip Hampton has an interesting set of articles at XML.com which are well worth reading.

There is also the dedicated Perl-XML Mailing list, which many here also frequent.

Recently the Perl-XML documentation site underwent an excellent upgrade, and there is lots of useful stuff in there aswell.

O'Reilly have some excellent books, including: ISBN 0596000588; ISBN 0596000537; ISBN 0596000464 and ISBN 0596001339 - also watch their New Books as XML is still running hot and news books come out frequently!

You will also discover that a few monks here also wrote some of the excellent XML modules available, and many of us have used them, so you should be able to get help fairly quickly should you need it.

Good luck!