On the JSLabs Blog today, there's a new tutorial walking you through the installation of the APC (Alternative PHP Cache) caching system for your PHP installation.
The Alternative PHP Cache (APC) is a free and open opcode cache for PHP. It was conceived of to provide a free, open, and robust framework for caching and optimizing PHP intermediate code.
The installation is pretty simple and, once you get things in place the configuration can start. The tutorial lists out several of the options you can use to customize your installation and a brief paragraph on what each of them do.