Please help me!
I don't know if it's possible to run the PHP ISAPI module within IIS 7 but you really should opt for a Fast CGI based solution as this is the Microsoft certified and supported way to run PHP on Windows (especially IIS 7).
Please see the following pages on learn.iis.net the official Microsoft IIS resource site.
A good url with installation instructions: http://blogs.iis.net/bills/archive/2006/09/19/How-to-install-PHP-on-IIS7-_2800_RC1_2900_.aspx
Official Instructions = http://in.php.net/manual/en/install.windows.php
You can also use Microsoft's new Web Platform Installer, as it will automatically install PHP, and configure it to run on your IIS server (as well as other apps such as Wordpress, etc). That's been the simplest solution I've seen to date.