I\'m new to mac os x. In the Windows XP world, there are packages available, like easyPHP, wampserver, uniformserver, that enable you to have a local webserver complete with php
XAMPP is also an excellent choice
Question : What means LAMP ?
Answer : Linux Apache MySQL PHP
Q: and if this was running on a Mac ?
A : try MAMP
Mac OS X is -- essentially -- Linux.
Mac OS X already contains Apache. Turn on file sharing and you'll turn on Apache.
You'll need to download and install MySQL for Mac OS X. http://dev.mysql.com/downloads/mysql/5.1.html
You'll need to edit the httpd.conf to enable mod_apache.
Five years later, i believe this question and existing answers still reading by some newcomers.
Personally, i strongly recommend using Homebrew to have a perfect development environment on mac os x. Not only PHP, homebrew opens wide all the doors to the open source toolkit/library/application heaven.
Here is my another answer related with this subject.
http://foundationphp.com/tutorials/php_leopard.php
http://dev.mysql.com/doc/refman/5.0/en/mac-os-x-installation.html
OS X comes with php and apache installed already. It doesn't have mysql installed by default, but you can easily download the Mac OS X version from the mysql website in either the tarball version or a package version.