This Tutorial shows how to install PHP after installing apache on windows. I'm going to use the msi installer in this Tutorial, you can get it from the PHP download page
I used the php-5.2.6-win32-installer.msi for this tutorial, but it should also work with new versions. Start by chosing a installation folder for PHP, i recommend c:\PHP\ for now.
Web Server Setup
Select the Web Server you wish To setup.
Simply chose the version you installed, if you followed the last Tutorial, then this is likely to be the Apache 2.2.x Module.
Apache Configuration Directory
Browse to select the directory containing the Apache Configuration Files
Chose the Conf directory in the installation folder of Apache.
Chose Items to Install
Simply chose the Extensions you need, and complete the installation. If you want to install MySQL later then i recommend you chose this extension. You may want to chose GD library to get access to the image function in php, this is called GD2 in the extensions list.
Seeing if it Works
Create a filename.php in your htdocs and enter the below code.
<?php echo phpinfo(); ?>
To see if it works, enter the URL for the file in your browser.
As a final step i recommend that you add index.php as the Directory Index, simply open httpd.conf and search for DirectoryIndex, change this line to index.php
The next Tutorial is Installing MySQL with Apache on Windows