mod_layout php

I'm trying to get mod_layout working with php and html files. I have html
files working just fine, but want to add php to it. Here is what I currently
have for one of my virtualhosts in Apache 2.

<VirtualHost *:80>
DocumentRoot "/var/www/html/website1"
ServerName website1.net
ServerAlias *.website1.net
CustomLog logs/website1.net-access_log urchin
AddOutputFilter LAYOUT html htm
LayoutHeader /var/www/html/utm.html
ErrorDocument 404 /index.html
</VirtualHost>

In my html file, I have:

<script src="http://ipaddress/__utm.js" type="text/javascript"></script>

How can I get php working with mod_layout?

SKeeter