my $cookie_jar = new HTTP::Cookies(file => "cookies.txt");
   $cookie_jar->load; END { $cookie_jar->save };

my $mech = new WWW::Mechanize( user_agent => "mp3slurpy/1.0", cookie_j
+ar => $cookie_jar );

$mech->get( $login_page );
$mech->submit_form(
    form_number => 3,
     fields      => {
       username    => 'mungo',
       password    => 'lost-and-alone',
     }
);

$mech->get( $mp3_file, ":content_file" => $output_file );
[download]

PS, there's no real reason to choose WWW::Mechanize over LWP::UserAgent except for the ease of using the API... Mech uses LWP though, so there's no disadvantage for picking it either.