If you need to easily set-up and maintain a local server environment on your Mac then look no further than MAMP. MAMP comes with Apache, MySQL and PHP and provides a local server environment that is independent of that installed as default by Leopard and best of all it’s free.
However, like any server environment, out-of-the-box you’re limited to a single local host. This can prove a little inconvenient if you’re developing more than one site and require more than one local host. The most convenient and cost effective way to overcome this limitation is to use virtual hosts.