From the Microsoft website:
To install PHP
Download the zip file from [external links are visible to admins only]. php .net / downloads.php, which contains the ISAPI filter for IIS.
Extract the contents of the zip file to C:\php.
Go to C:\php.
Copy the php.ini-dist file to your system root (the directory where you installed Windows), rename it to php.ini, and edit it to fit your needs.
Start the Microsoft Management Console or the Internet Services Manager, located in Control Panel.
Click your Web server, and select Properties.
If you want to perform HTTP authentication using PHP, add a new ISAPI filter under ISAPI Filters. Use PHP as the filter name, and supply a path to php4isapi.dll.
Under Home Directory, click Configuration. Add a new entry to Application Mappings. Enter the path to php4isapi.dll as the Executable, enter .php as the extension, leave Method exclusions blank, and select the Script engine checkbox.
Stop IIS completely:
net stop iisadmin /y
Start IIS again:
net start w3svc
You can also perform this installation via command line using the ADSI object model for IIS.
To test PHP
• Create a file called test.php with the following code to check for PHP support:
<? phpinfo(); ?>
The file needs to be located in the document root path, which should be set up by default to C:\ inetpub\ wwroot\ lamp.
Hope this helps-