It's hard to answer this question without seeing the data structure, but here are a few clues.

Use Data::Dumper to see what the hash looks like:

use Data::Dumper;
print header('text/plain');
print Dumper($foo);
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If you use forcearray when parsing the XML:

$foo = XMLin($xml, forcearray => 1);
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Then you can access the data in a structure like this (which is exactly what Dumper prints):

$foo = {
 'INFO' => [
            {
             'lastchecked' => '20010506070758',
             'content' => 'Rendered by the Newest Nodes XML Generator'
+,
             'site' => 'http://perlmonks.org',
             'sitename' => 'Perl Monks'
            }
           ]
       };
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With loops like this:

if(defined @{$data->{'INFO'}}){
   for my $when(@{$data->{'INFO'}}){
      $lastcheck = $when->{'lastchecked'}
      }
   }
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Super search around perlmonks a bit for more info.