Replace random image with a php include

I know enough php to get myself in trouble..

I'm trying to create a header that allows linkable photo credits on the header images
(I used a "PHP Text / Banner RandomRotator" script from http://www.stevedawson.com/download.php)

I've got the random.php script to pull html from a .txt file (includes html, images and css - but no body tags or doc type). This works fine when I create a simple php include file to test it out on my server. I cannot figure out how to make it work in order to replace the stock marinelli image rotation on my drupla set up.

With my files in the directory I've tried replacing a line of the graphics.css code:
#header {background: #000033 url(img/banners/rotate.php) no-repeat 0px 0px;}
with
#header {background: #000033 url(img/banners/random.php) no-repeat 0px 0px; }

I've also tried to insert :

<?PHP include "img/banners/random.php" ?>

directly below the
<div id="header">on the page.tpl.php

any suggestions on how to make this work?

please and thankyou