Download the Windows PHP binary package from http://www.php.net/downloads.php

Extract to a temporary directory

Copy the following files to the directory you want PHP to live (paths with spaces are not recommended, ie c:\program files)

php.ini-recommended (rename to php.ini) - php.ini-dist can be used depending on your requirements php4apache2.dll or php5apache2.dll php4ts.dll or php5ts.dll

Modify php.ini to have the following doc_root = c:\apache2\htdocs (or wherever your document root for PHP happens to be)

Add your PHP home directory to the Windows PATH (eg, c:\php)

Add the following to [apache directory]/conf/httpd.conf (modify as required)

For PHP 4 do something like this:

LoadModule php4_module "c:/php/php4apache2.dll"
AddType application/x-httpd-php .php

For PHP 5 do something like this:

LoadModule php5_module "c:/php/php5apache2.dll"
AddType application/x-httpd-php .php

configure the path to php.ini

PHPIniDir "C:/php"

If you are using PHP override settings, make sure overrides are allowed in your Apache httpd.conf configuration file. There should be an AllowOverride command.

Note: you only need a small subset of the files in the download if you just want to run PHP.