Requirements:

Apache2 - http://httpd.apache.org/download.cgi
PHP5 - http://www.php.net/downloads.php

Setup

Follow the installation instructions for each version.

Install PHP to C:\php
Install Apache to the default location

Configuration

Open up the Apache configuration file
 C:\Program Files\Apache Group\Apache2\conf\httpd.conf
Find the LoadModule settings and add in the following line
 LoadModule php5_module "c:/php/php5apache2.dll"
Search for DirectoryIndex and add in some php references (if you are using .php files)
 DirectoryIndex index.html index.html.var index.php
Then search for the AddType entries and below them add the following 2 lines:
 AddType application/x-httpd-php .php .html
 PHPIniDir "C:\php"
Now restart Apache and create a page called test.php in the htdocs directory
(C:\Program Files\Apache Group\Apache2\htdocs\)
Add the following code in php tags:

 phpinfo();

and then open up a browser and go to
http://localhost/test.php
Well done! You should see a page with all the php information on.
End