There's an advantage to XPath in that one can easily extract specific nodes that have specific attributes and get the specific component (i.e., a node in xml format or text within a tag) that one wants in a string.  Of course, you're probably right, if I knew more about what I'm doing I could work with just LibXML.  Nevertheless, with the help of the lovely and talented Miss jarich, I managed to resolve the problem, or should I say, I patched together LibXML and XPath to accomplish what I wanted.  Below is code added to the original node above that resolved the problem:

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use XML::LibXML;# Plus the other modules above
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my $uri = "http://www.perlmonks.org/index.pl?node_id=30175&sinceunixti
+me=20020820";
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# 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.]
[download]

There are three key changes here.  First, I had to change the URI address.  The uri I started with was a little messy:  I kept getting all kinds of extra HTML header stuff I couldn't skip over, causing it to crap out--I was probably doing it wrong, I admit.  Incidentally, the unixtime value should be calculated by code--I'll tend to that later.  The second key is to use the toString directive to save the matching XML tags and their text contents to $file.  The last and most significant key was to change the last line of the code shown in this post from the "filename" format directive (XML::XPath->new(filename=>$file))to the "xml" directive (XML::XPath->new(xml=>"$file")).  So, LibXML gets the XML from the PM site and then saves it to a string for XPath to read and extracts the desired nodes for standard Perl to work with.  I know this is the hard way to do it, but I'm still learning and would love for any one who so inclined to stream-line what I've done.  Otherwise, thanks for all the feedback and advice.

-Spenser

That's Spenser, with an "s" like the detective.