What happen about xml in xampp?

[destiny_cores]

This is my code
<?php

$xml_filename="simple.xml";

$dom=new DOMDocument;
$dom->load($xml_filename);

?>
i use xampp 1.5.3a
when i run this, it show error:
Fatal error: Call to undefined method domdocument::load() in D:\Apache Group\Apache2\htdocs\xsltest\xml_xslt.php on line 8

how to solve this?

thanks you