codice:
$query = "SELECT id, link
          FROM download 
          WHERE idn = '$idn'"; 
$result = mysql_query($query, $db); 

$row  = mysql_fetch_array($result); 

$link = $row["link"]; 
$id   = $row["id"];  

$query = "UPDATE download SET 
          dlc = dlc + 1 , data = NOW()
          WHERE id = '$id'"; 

mysql_query($query, $db); 
mysql_close($db);

header ("Location: $link");
exit;
?>
Poi...
codice:
......
$query = "SELECT dlc FROM download WHERE idn = '$idn'"; 

$result = mysql_query($query, $db); 

$pippo = mysql_fetch_assoc($result);
echo $pippo['dlc']; 
?>
Ma perche' mai hai paura di usare la chiave primaria.... quello e' un puro dato inutile.