Script not retrieving PhP variables

[Anon]

Hi,
I am a newbie and using windows version php4.2.2 running on IIS. I've created a sample php script to display PhP environment variables but it just display the labels without the variables information. Could someone please point me to the right direction. Enclosed is my sample script.

<?php
// My first test php script
echo "<pre>";
echo "Browser :$HTTP_USER_AGENT";
echo "Host :$HTTP_HOST";
echo "</pre>";
?>

Thanks.
Cheers, Lennie