Non è molto bello ma sembra funzionare.

File menu000.php

Codice PHP:
<LI id='menu1'    class='inactive'>Menù 1</LI>
<LI id='contatti' class='inactive'>Contatti</LI>
<LI id='menu2'    class='inactive'>Menù 2</LI>
<LI id='menu3'    class='inactive'>Menù 3</LI>
<LI id='menu4'    class='inactive'>Menù 4</LI>
<script language="JavaScript" type="text/javascript">
<!--
document.getElementById('<?php print $id_active ?>').className = 'active';
//-->
</script>


File test813.php
Codice PHP:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Untitled</title>
<style type="text/css">
<!--
.active   {background-color:red}
.inactive {background-color:yellow}
-->
</style>
</head>
<body>
<?php 
 $id_active = 'contatti';
 include('menu000.php');
?>
</body>
</html>