The makers of EasyPHP, an all-in-one Apache, PHP, and MySQL installer for Windows, also provides a PHP 6 version if you’re interested in experimenting with the next major version of the language (as I demonstrate in my PHP 6 and MySQL 5 for Dynamic Web Sites book). I haven’t personally used EasyPHP (I try to avoid using Windows, if at all possible), but from what I can tell it seems to be a quality, well-supported product. EasyPHP is available for free although donations are encouraged.