r.joseph,
I've done some work with XML so maybe I can point you to a few of the resources I used. First of all, I've written a simple XML tutorial that is online here. Unfortunately, I haven't yet added a section on XML and Perl, but you can pick up the basics of XML. It does, however, cover XML interfaced with HTML, JavaScript, & CSS. Hopefully, if time ever permits, I'll get Perl in there, too. I also used XML By Example, by Benoit Marchal, to learn XML, but I wasn't overly thrilled with that book. However, it worked. :)

If you're interested in using XML with Flash (I know you said this was your friend's work, but I wasn't sure if you were looking for material on this as well), I can recommend a few good books. Foundation ActionScript, by Sham Bhangal, Flash 5 Dynamic Content Studio, by David Beard, and a new upcoming book Flash 5 ActionScript Studio, by Brendan Dawes, et al. These books are all published by FriendsOfEd and, as far as I'm concerned, are some of the best books on Flash out there.

I'm currently working on a scheduling system that uses XML to store all the data input by a client and then display that content dynamically to a site reader, so I'm fairly familiar with using XML::Parser to get data in and out of XML, so if you have any questions trying to interface Perl with XML, just let me know - I'd be happy to help.

If you'd like to take a look at the scheduling system, to see how I'm using it, I'd be happy to show you the code and give you links to the site, just /msg me. (That goes for anyone else that might be interested, as well.)

Good luck to you!

- Sherlock

Skepticism is the source of knowledge as much as knowledge is the source of skepticism.