I appreciate that you said you cannot install CPAN modules, but you could at the very least use some of the pure-Perl XML parsing modules (even copying and pasting the code into your program, if worse comes to worse).

You could try this: XML::Parser::Lite::Tree or this: http://www.kawa.net/works/perl/treepp/treepp-e.html (but you might have to solve manually some dependencies on your very old version of Perl). They certainly don't have all the bells and whistles of full-fledged heavy-weight Dom or Sax XML parsers, but they may possibly get you out of trouble.