scusami ma sono dovuto scappare al lavoro prima.
comunque ora va! con il codice così funziona tutto:

Codice PHP:
<?php
    include "config.inc.php";
    
    $dati=mysql_fetch_array(mysql_query("SELECT * FROM ambulatori WHERE id=1"));
          
    mysql_close($db_conn);

  ?>

    <form method="post" action="insert.php">
     <table>
           
      <tr>
       <td>Nome</td>
       <td><input type="text" name="nome" size="20" maxlength="30" value="<?php echo $dati['nome'] ?>" /></td>
      </tr>
      
      <tr>
       <td>Telefono</td>
       <td><input type="text" name="tel" size="20" maxlength="10" value="<?php echo $dati['tel'] ?>" /></td>
      </tr>
    
     </table>

    
     <table>
      
      <tr>
       <td>Luned&igrave; mattina</td>
       <td><input type="text" name="lun_matt" size="15" maxlength="15" value="<?php echo $dati['lun_matt'] ?>" /></td>
      </tr>
      
      <tr>
       <td>Luned&igrave; pomeriggio</td>
       <td><input type="text" name="lun_pom" size="15" maxlength="15" value="<?php echo $dati['lun_pom'] ?>" /></td>
      </tr>
      
      <tr>
       <td>Marted&igrave;</td>
       <td><input type="text" name="mar" size="15" maxlength="15" value="<?php echo $dati['mar'] ?>" /></td>
      </tr>
      
      <tr>
       <td>Mercoled&igrave;</td>
       <td><input type="text" name="mer" size="15" maxlength="15" value="<?php echo $dati['mer'] ?>" /></td>
      </tr>
      
      <tr>
       <td>Gioved&igrave;</td>
       <td><input type="text" name="gio" size="15" maxlength="15" value="<?php echo $dati['gio'] ?>" /></td>
      </tr>
      
      <tr>
       <td>Venerd&igrave;</td>
       <td><input type="text" name="ven" size="15" maxlength="15" value="<?php echo $dati['ven'] ?>" /></td>
      </tr>
     
     </table>

     
     <table>
      
      <tr>
       <td colspan="2"><input type="submit" value="Modifica" /></td>
      </tr>
     
     </table>
      
    </form>
stampa tutto correttamente nei campi.
grazie mille dell' aiuto pippuzzo!