If you are going to develop plugins for WordPress, you need WordPress itself and an environment that can run it. Download the latest version of WordPress from http://wordpress.org/download. It is then just a matter of fiding a suitable place to install it.

WordPress 3 runs on a web server (most commonly Apache) that can run at least PHP 4.3 and MySQL 4.1.2—WordPress 3.2 requires PHP 5.2 and MySQL 5.0.15. Since both PHP and MySQL are widespread web technologies and WordPress is such a popular blogging tool, most hosting providers can support running WordPress on
their servers. If in doubt, consult your web host’s FAQ.
Another option is to run WordPress in a «sandbox» environment on your own computer. This can be more involved since you have to set up your computer as a web server and confiure several other inter-related technologies, but thankfully there are bundled packages available that do much of the diffiult work for you—we have listed a few options for these types of packages below.
A third option is to run a virtual machine on your local computer using emulation software like Parallels (http://www.parallels.com), VMware (http://www. vmware.com) or VirtualBox (http://www.virtualbox.org). This can be a great way to mimic your intended production environment precisely and still get all the benefis of hosting your site locally, but it does require some solid system administration skills, so this option is mainly recommended for seasoned developers.