I was installing PHP 5 on an IIS 6 server when I ran into what turns out to be a pretty common problem. PHP appeared to be installed correctly, but browsing to any page with a .php extension returned a 404 Page Not Found error. While the steps below fixed this for me, I had to piece them together from a few different sources, and a number of other suggestions (like copying the php.ini file to C:/WINDOWS/) didn’t work and were not necessary.

Open your IIS management console at C:\WINDOWS\system32\inetsrv\iis.msc.
Drill down to your web site, right-click and select Properties.
Select the Home Directory tab, then click on the Configuration button.
Select the Mappings tab. If you don’t see a .php extension listed, click the Add button. Browse to the PHP 5 DLL (which may be at C:\Program Files\PHP\php5isapi.dll). Type .php into the Extension field and leave everything else at the default values. Click OK. The extension and executable path will be filled out and under Verbs you should see “All”.

I should point out that I didn’t have anything listed under the ISAPI Filters tab.

Stop and restart your IIS server and browse to a .php file. (To restart your IIS server, open the IIS management console, right-click the local computer in the left pane, hover on All Tasks and choose Restart IIS.) Chances are, you’re no longer getting the 404 error, but are now seeing a 403.1 message, like:

The page cannot be displayed
You have attempted to execute a CGI, ISAPI, or other executable program from a directory that does not allow programs to be executed.

Please try the following:

* Contact the Web site administrator if you believe this directory should allow execute access.

HTTP Error 403.1 – Forbidden: Execute access is denied.
Internet Information Services (IIS)

Open iis.msc again, go back to the Home Directory tab, and select the “Scripts only” option from the Execute Permissions menu. Restart the server.

The server should now be correctly processing .php files.