As you've learned in previous chapters, the symfony framework is a set of files written in PHP. A symfony project uses these files, so installing symfony means getting these files and making them available for the project.
Being a PHP 5 framework, symfony requires PHP 5. Make sure you have it installed by opening a command line and typing this command:
> php -v PHP 5.2.0 (cli) (built: Nov 2 2006 11:57:36) Copyright (c) 1997-2006 The PHP Group Zend Engine v2.2.0, Copyright (c) 1998-2006 Zend Technologies
If the version number is 5.0 or higher, then you're ready for the installation, as described in this chapter.