On the Symfony blog there's a recent post showing how to integrate the framework with Doctrine 2 via the sfDoctrinePlugin:

Today I am happy to tell you that this version of sfDoctrinePlugin is now available and ready for you to use. This article will give you a little information about how you can get started using it today!

Installing and enabling the plugin is as easy as a svn checkout and changing a few settings in your project's configuration files. You can then define your database connection and schema information settings so that the rebuild ("symfony doctrine:build") will build out correctly. They include a simple example, a repository class, to let you be sure everything is up and working correctly. You can find more information about Doctrine 2 from its online manual.