Intendevo un'ottimizzazione ancora più grande 
Così:
Codice PHP:
$query = "SELECT F.file,F.voto,
U.nick
FROM mp3 AS F,
utenti AS U
WHERE F.iduser = U.id
ORDER BY F.voto DESC
LIMIT $start,$step";
$result = mysql_query($query, $db);
$pos = $start;
echo '<table border="1"><tr><td>posizione</td><td>nickname</td><td>voto</td><td>file</td></tr>';
while ($row = mysql_fetch_array($result))
{
$pos = $pos + 1;
echo '<tr><td>';
echo $pos;
echo '</td><td>';
echo $row['nick'];
echo '</td><td>';
echo $row['voto'];
echo '</td><td>';
echo $row['file'];
echo '</td></tr>';
}
echo '</table>';