That's a better suggestion than mine :-). In fact I recall doing exactly that for another site! 'Course, I only recall it now...
------8<--------index.htm------------
<HEAD>
<SCRIPT language="JavaScript1.1">
<!--
location.replace("index.php");
//-->
</SCRIPT>
<NOSCRIPT>
<META http-equiv="Refresh" content="0; URL=http://www.your.site/index.php">
</NOSCRIPT>
</HEAD>
<BODY>
Some sort of splash page, including a link to index.php incase none of the automatic redirection works.
</BODY>
----------------->8--------------