.
.
use XML::LibXML;
# Plus the other modules above
.
.
my $uri = "http://www.perlmonks.org/index.pl?node_id=30175&sinceunixtime=20020820";
.
# Parse out XML using LibXML to a string
my $doc = $parser->parse_file($uri);
my $root = $doc->getDocumentElement;
my $file = $doc->toString;

my $xpath = XML::XPath->new(xml=>"$file");

[...And resume the above code.]