Dynamic Value From A Form Inside Of Iframe Not Changing?

pageone.htm has an iframe with pagetwo.htm inside pagetwo has a form with a hidden field that has a dynamic value.I'm trying to get that value from pageone.htm using:var myid = window.frames['myiframe'].document.forms['myform'].elements['page'].value; This is working, but I just get the value that the field had when I did:

setInterval('alert(GetValue())', 9000);

for the first time. All the alerts after the first one have the same value even when myid is changing in pagetwo.htm (tested alerting it in there).I thought that by using setInterval I would be checking for a fresh value every 9 seconds but what I get is the same old value every 9 seconds

///// pageone.htm /////
<script type="text/javascript">
function GetValue() {[code]......