Adding PHP to the header

[rootnik]

I have a set of PHP scripts that formats and displays dynamic xml data in nice little HTML tables...

I want to include these in my header.

I've searched around and found how to add the PHP to templates, but I can't find the actual PHP file the header is in.

If I read everything correctly I want to add this:

PHP Code:

<?php
ob_start();
include 'displayxml.php';
$displayxml = ob_get_contents();
ob_end_clean()
?>

to WHAT file?

(and then place $displayxml in my header template)