ต้องการ เลือกสินค้าใน list box และให้แสดงผลในอีกหน้าวินโดว์นึงค่ะ แต่ทำไม่ได้สักที งงมากค่ะ

<?php


$product_id=$_GET['product_id'];


 if($product_id == "entree1")
 {
		
	  $t1=$_POST['TomYumGoong'];
      $product_name = "Tom Yum Goong";
      $product_class = "Soup";
      $product_meat = $t1;
      $unit = "200";
      $priceperunit = "9.00";
	  

 $product_title = $product_class." - ".$product_name." (".$product_meat.") ";

 }


?>

<? if($unit >0) { ?>


<p> Your selecte size is: <?php echo $t1 ?></p>                                    
<form action="cart.php" method="post" onSubmit="return checkform(this,<? echo $unit; ?>);">

<input name="add" type="hidden" value="<? echo $product_title; ?>">
<input name="price" type="hidden" value="<? echo $priceperunit; ?>">
<input type="hidden" name="product_id" value="<? echo $product_id; ?>">

<table border="1" cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 1px dashed #800000" bordercolor="#111111" width="90%" id="AutoNumber1">
  <tr>
    <td width="34%" style="border: 1px dashed #800000">
 <p align="right"> Quantity:&nbsp;&nbsp; </p> </td>
 <td width="66%" style="border: 1px dashed #800000">&nbsp;&nbsp;<input name="qty" type="text" size="36" maxlength="5" id="text-select"></td>
  </tr>
  
<tr>
    <td width="100%" colspan="2" style="border: 1px dashed #800000">
    
    <input type="button" value="Back to menu"  onClick="javascript:window.close()" id="text-button"/>
    <input type="submit" value="Add to cart" name="submit" id="text-button"></td>

  </tr>
</table>
</form>
             


<? }
else {
      echo "<center>
<table border=\"1\" style=\"border-style:dotted; border-collapse: collapse; padding-left:4; padding-right:4; padding-top:1; padding-bottom:1\" bordercolor=\"#111111\" width=\"75%\" id=\"AutoNumber1\" height=\"138\">
  <tr>
    <td height=\"136\">
    <center>
    <font size=\"5\" color=\"#ffffff\">Sorry, product is out of stock.</font><br>
    </center>    
    </td>
  </tr>
</table>

</center><br>";
}
?>

</body>
</html>