The best way to install and configure a Symfony2 project is described in the official documentation as follows:
Mac OS X / Linux
$ sudo curl -LsS http://symfony.com/installer -o /usr/local/bin/symfony
$ sudo chmod a+x /usr/local/bin/symfony
Windows
c:\> php -r "file_put_contents('symfony', file_get_contents('https://symfony.com/installer'));"
Then you could use the Symfony binary to build the right scaffolding:
$ symfony new my_project