Magento displays same page inside the visible page when trying to send/receive data from another php -

i'm trying make new functionality on custom back-end module i've created few weeks ago. new functionality consists in making query in order list in 'select-option' data specific customer. then, when select 1 of these options, i've made script catch option, send get method .php, , then, php makes data selected , makes echo whatever.

the code following (data.phtml):

<script language="javascript" type="text/javascript">     function showpresu(str){     if (str=="")     {     document.getelementbyid("txthint").innerhtml="";     alert('nothing here');     return;     }     if (window.xmlhttprequest)     {// code ie7+, firefox, chrome, opera, safari         xmlhttp=new xmlhttprequest();         alert('makes request');     }     else     {// code ie6, ie5         xmlhttp=new activexobject("microsoft.xmlhttp");         alert('new object');     }     xmlhttp.onreadystatechange=function()     {         if (xmlhttp.readystate==4 && xmlhttp.status==200)         {             document.getelementbyid("txthint").innerhtml=xmlhttp.responsetext;         }     }     xmlhttp.open("get","receiveselection.php?q="+str,true);     xmlhttp.send();     }     </script> 

as can notice i've written alerts in order make sure code enters inside script.

the select/option following(data.phtml):

echo '<select name="presus" onchange="showpresu(this.value)">';     for($n=1;$n<=$h; $n++){         echo "<option value='$status_id[$n]'>$status_id[$n]";     }     echo "</select>"; 

$status_id[$x]: it's array contains data i've introduced @ beginning.

and div final data has displayed (data.phtml):

<div id="txthint"> <b>result info listed here.</b> </div> 

and finally, php has interact info send via method get (receiveselection.php, in same folder data.phtml. notice php changed code, mean, change following code make query, making tests it's ok):

<?php $q=$_get["q"]; echo $q; ?> 

the issue is, when try show 'receiveselecton.php' in div created so, instead of watching result of 'receiveselection.php' appears same magento page in moment before (data.phtml), mean, appears same page twice, 1 'normal' , other inside div.

does know how call receiveselection.php instead of creating data.phtml?

edit: if put code outside magento works, inside not. problem maybe incoherence magento don't know. or if knows better way it, please tell me.

i tried code in sustem working fine.. problem figured out request sending not able reach file receiveselection.php

solution problem can create controller action receiveselection.php lets receiveselectionaction change code this

xmlhttp.open("get","your_module/your_controller/receiveselection.php?q="+str,true);