Pagina dinamica in PHP e somma?

[Xnetus]

Prova a fare in questo modo:

<form method="POST" action="index.php" name="form1">
      <table width="98%" border="0" align="center" cellpadding="5" cellspacing="0">
        <tr>
          <td><span class="Stile3">*</span> Campi obbligatori</td>
          </tr>
      </table>

      <table width="98%" border="0" align="center" cellpadding="5" cellspacing="0">
        <tr>
          <td width="134" class="Stile5">Foto</td>
          <td valign="top" class="Stile5">Descrizione - Codice - Prezzo/cad.</td>
          <td width="50" valign="top" class="Stile5">Quantità</td>
        </tr>
      </table>      
      <table width="98%" border="0" align="center" cellpadding="5" cellspacing="0">
        <tr>
          <td width="134">[img]../maschere/oro.jpg[/img]</td>
          <td valign="top" class="Stile5">Nome (Cod.201)</td>
          <td width="50" valign="top">
            <select name="p1" onChange="form1.submit()">
            <option value="<? echo $_POST['p1']; ?>" selected><? echo $_POST['p1']; ?></option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
            <option value="6">6</option>
            <option value="7">7</option>
            <option value="8">8</option>
            <option value="9">9</option>
            <option value="10">10</option>
            </select>
          </td>
        </tr>
      </table>
      <table width="98%" border="0" align="center" cellpadding="5" cellspacing="0">
        <tr>
          <td width="134">[img]../maschere/oro.jpg[/img]</td>
          <td valign="top" class="Stile5">Nome (Cod.201)</td>
          <td width="50" valign="top">
            <select name="p2" onChange="form1.submit()">
            <option value="<? echo $_POST['p2']; ?>" selected><? echo $_POST['p2']; ?></option>
            <option value="1">1</option>
            <option value="2">2</option>
            <option value="3">3</option>
            <option value="4">4</option>
            <option value="5">5</option>
            <option value="6">6</option>
            <option value="7">7</option>
            <option value="8">8</option>
            <option value="9">9</option>
            <option value="10">10</option>
            </select>
          </td>
        </tr>
      </table>
      <?
      $cost1= $_POST['p1'] * 200;
      $cost2= $_POST['p2'] * 100;
      $sum = $cost1 + $cost2;
      ?>
      Totale= <? echo "$sum"; ?>  
</form>