Many web developers want to run Apache and PHP on their own computer since it allows them to easily test their scripts and programs before they put them "live" on the Internet. This article gives a step by step guide on how you can install and configure PHP5 to work together with the Apache HTTP Server on Windows. The procedure has been tested to work on both Windows XP and Vista.
Installing PHP on your development PC allows you to safely create and test a web application without affecting the data or systems on your live website. This article describes PHP installation as a module within the Windows version of Apache 2.2. Mac and Linux users will probably have it installed already.
If your server has activated support for PHP you do not need to do anything. Just create some .php files, place them in your web directory, and the server will automatically parse them for you. You do not need to compile anything or install any extra tools. Because PHP is free, most web hosts offer PHP support.
Although an installer is available from php.net, I would recommend the manual installation if you already have a web server configured and running.