Hi guys im trying to get this simple page to work and i dont know why it does not owrk. im new to ajax


i crreated a form and then i use ajax to call a php script which prints out options for the select.

however when i submit my php can not capture the values! but my js sees the value, i use and alert to display it when it is changed and it shows the appropriate value. forexample $_POST['testing']


Code:
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> 
<html xmlns="http://www.w3.org/1999/xhtml"> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<title>Untitled Document</title> 

<script language="javascript"> 
    function checking() 
    { 
        var xmlHttp = false; 
        try 
        { 
            xmlHttp = new ActiveXObject("Msxml2.XMLHTTP"); 
        }    catch(e) 
        { 
            try 
            { 
                xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); 
            }    catch(e) 
            { 
                try 
                { 
                    xmlHttp = new XMLHttpRequest(); 
                }    catch(e) 
                { 
                    altert("your browser is too old") 
                } 
            } 
        } 
         
        var obj = document.getElementById("testing"); 
         
        xmlHttp.open("GET","select.php"); 
         
        xmlHttp.onreadystatechange = function() 
        { 
            if(xmlHttp.readyState == 4) 
            { 
                obj.innerHTML = xmlHttp.responseText; 
            } 
        } 
         
        xmlHttp.send(null); 
    } 
     
    function castvalue(v) 
    { 
        alert(v); 
    } 
         
</script> 

<? 
    if($_POST['submit']) 
    { 
        echo("Testing: - " . $_POST['testing'] . " -"); 
    } 
?> 

</head> 

<body onload="checking();"> 
    <form method="post"> 
        <select id="testing" onchange="castvalue(this.value);"> 
            <div id="grab" name="grab"> 
            </div> 
        </select> 
        <input type="submit" id="submit" name="submit" value="submit" /> 
    </form> 
</body> 
</html>

select.php

PHP Code:
Code:
<? 
    include("../include/cms/connect.inc.php"); 
             
    $platformlist = "SELECT * FROM platform"; 

    $myplatformlist = mysql_query($platformlist) or die(mysql_error()); 
     
    while($queryplatformlist = mysql_fetch_array($myplatformlist)) 
    { 
            echo  "            <option value=\"" . $queryplatformlist["id"] . "\">" . $queryplatformlist["name"] . "</option>"; 
    } 
     
    mysql_free_result($myplatformlist); 
    mysql_close();     
?>

Plz plz help me~