newbie: having problem even with my first xml script

dear friends,

just started a book "Teach yourself xml in 24 hours".

The first example is not working.

it goes like this

in the first chapter there is one simple xml file>>

<?xml version="1.0"?>
<MESSAGE>
<TO>STUDENT</TO>
<FROM>AUTHOR</FROM>
<SUBJECT>INTRODUCTION TO XML</SUBJECT>
<BODY>WELCOME TO XML!</BODY>
</MESSAGE>

then contents of this file called from a html file>>>

<html>
<head>
<script language=javaScript>
var RootElement1;
var xmlDoc1=new ActiveXObject("microsoft.xmldom");
xmlDoc1.load("listing.xml");

function StartUp()
{
if (xmlDoc1.readyState="4")
{
StartLoading();
}
else
{
alert("Loading operation could not start");
}
}

function StartLoading()
{
RootElement1=xmlDoc1.documentElement;
todata.innerText = RootElement1.childNodes(0).text;
fromdata.innerText = RootElement1.childNodes(1).text;
subjectdata.innerText = RootElement1.childNodes(2).text;
bodydata.innerText = RootElement1.childNodes(3).text;
}

</script>
</head>
<body bgcolor="ffffff" onLoad = "StartUp()">
TO: 
FROM: 
SUBJECT: 
BODY: 
</ body>
</html>

Can anyone tell me why it is not working, and where i am going wrong.

thank you very much in advance.