Doctrine has been integrated into symfony with the sfDoctrinePlugin:

http://www.symfony-project.org/plugins/sfDoctrinePlugin

Doctrine's manual is on:

http://www.doctrine-project.org/documentation/manual/1_1/en

Autoloading Doctrine in Zend Framework:

http://weierophinney.net/matthew/archives/220-Autoloading-Doctrine-and-Doctrine-entities-from-Zend-Framework.html