Working on it...
I've got PHP 4 and PHP 5 installed on my local server (IIS 5.1). I installed PHP 4, moved php.ini from the Windows folder to the PHP4 folder, repeated that process for PHP 5, then manually edited the IIS scriptmap settings so .php is PHP 5 and .php4 is PHP 4.
Then, to make RdMIse work, I copied php_domxml.dll and iconv.dll from a PHP zip package to the PHP 4 folder, and added the domxml entry to php.ini. I created "rdmi.php4", which just includes the real rdmi.php to make it run under PHP 4.
I'm aiming to have the next version of RdMise working on Apache/PHP4, IIS/PHP4, and IIS/PHP5. A SitePoint post I found has lot of reasons why people aren't moving to PHP5.
Feedback is closed. Feel free to contact me privately.