The three PHP libraries in the Symfony Components PHP library -- YAML, Templating, and Event Dispatcher -- were once an integrated part of the Symfony project, but now they represent a separate Symfony project. Because the Symfony Components are standalone PHP classes, you can both use them without the Symfony MVC framework and integrate them very easily in any PHP project. In her PHPBuilder article, Octavia Andreea Anghel teaches you how to work with them.
You can install each of the Symfony Components in the same, very simple manner. All you need to do is download the source code (a TAR or a ZIP archive) from the project page. Anghel explains the rest.