Prova cosi:

Codice PHP:
<?php
$ricerca 
= isset($_POST['titolo']) ? $_POST['titolo'] : FALSE;
$dim = isset($_POST['dim']) ? $_POST['dim'] : FALSE;

$dati mysql_query("SELECT num, dim, titolo, pcover FROM films WHERE dim ='$dim' limit 0,10");
while(
$arr mysql_fetch_array($dati)){
           echo 
"<tr><td id='ris'>$arr['num']</td>
                     <td id='ris'>
$arr['dim']</td>
                     <td id='ris'>
$arr['titolo']</td>";
                  if(
$arr['pcover'])
                     
$pcover $arr['pcover'];
                     echo
"<td id='ris'>[img]$pcover[/img]</td>
                 </tr>"
;
                  else echo
"<td class='noimg'></td>
                 </tr>"
;
}                        
?>
Testa e dimmi se funge.