Surprisingly enough, I've tried this script into another platform but 
+same system. In a macbook santa rosa with an Ubuntu 8.04 partition , 
+it works both in Leopard (Mac OS X) and Ubuntu 8.04 partitions.

So I guess the problem I have is specific of the PC I'm running it. An
+yone any idea of commands that can help me checking the differences b
+etween the Ubuntu partition on the macbook and the Ubuntu partition o
+n the PC (which are supposed to have same packages)?
[download]

Monks sorry for bumping , I'd like to know if my code works for most of you in order to try to find where's the problem of my PC. Thanks!

Most of us don't use Gmail :)
Compare the difference between systems, perl versions, module versions. You could take snapshots on each system with CPAN, and compare (snapdiff -- Compare CPAN autobundle files)

cpan> autobundle Snapshot
...
Wrote bundle file
    ...Bundle\Snapshot_2008_10_27_00.pm
[download]

same with CPANPLUS

cpanp b
Wrote autobundle to '...5.10.0\dist\autobundle\Snapshot_2008_10_27_02.
+pm'
[download]

or use Devel::Modlist

perl -d:Modlist foobar.pl
...

AutoLoader             5.63
Carp                   1.04
Config
DynaLoader             1.05
Exporter               5.58
HTML::Element          3.16
HTML::Entities         1.29
HTML::Parser           3.45
HTML::Tagset           3.04
HTML::TreeBuilder      3.13
integer                1.00
vars                   1.01
warnings               1.03
warnings::register     1.00
[download]

or scandeps.pl (Module::ScanDeps)

scandeps foo.pl
'HTML::Element'     => '3.16',
'HTML::Tagset'      => '3.04',
'HTML::Entities'    => '1.29',
'HTML::Parser'      => '3.45',
'HTML::TreeBuilder' => '3.13',
[download]