IIS problem while using PHP

I have set up a site using PHP that works fine when using apache. Under IIS, I get to the initial logon page, but after clicking anything I get the HTTP 405 - Resource not allowed error. If I go to the site by typing the URL with the default file name (index.php) attached to the end, then everything works fine. Is there some sort of redirect problem. I've followed all the installation instructions and I have other PHP sites on the same server that are configured the same way but run fine. I'm at a loss??? Thanks for any help you can give!