I've never used XML::RSS, but the XML::RSS docs state:

channel (title=>$title, link=>$link, description=>$desc, language=>$language, rating=>$rating, copyright=>$copyright, pubDate=>$pubDate, lastBuildDate=>$lastBuild, docs=>$docs, managingEditor=>$editor, webMaster=>$webMaster)

I can only assume that 'pubDate' is short for 'publication date', given the two times it occurs in the documentation. The other time, there's a mention of 'date' under 'dc' (short for Dublin Core), and shows the format is an ISO date:

 use XML::RSS;
 my $rss = new XML::RSS (version => '1.0');
 $rss->channel(
   title        => "freshmeat.net",
   link         => "http://freshmeat.net",
   description  => "the one-stop-shop for all your Linux software need
+s",
   dc => {
     date       => '2000-08-23T07:00+00:00',
     subject    => "Linux Software",
     creator    => 'scoop@freshmeat.net',
     publisher  => 'scoop@freshmeat.net',
     rights     => 'Copyright 1999, Freshmeat.net',
     language   => 'en-us',
   },
   syn => {
     updatePeriod     => "hourly",
     updateFrequency  => "1",
     updateBase       => "1901-01-01T00:00+00:00",
   },
   taxo => [
     'http://dmoz.org/Computers/Internet',
     'http://dmoz.org/Computers/PC'
   ]
 );
[download]

Update: From your later responses, it seems that the issue isn't just what the correct keys and formats to the value are when using XML::RSS, but that you're not actually familiar with RSS. You may wish to read the RSS 2.0 specification, and if you're dealing with RSS 0.9 or 1.0, the notes on RSS in the RDF primer. Even w3schools has a lesson on it. (I haven't worked w/ RSS in years, and back then, I just generated it by hand)