If you want a quick way of getting Doctrine 2 working with CodeIgniter 2, you can download a pre-configured installation from my GitHub repository. There are currently three branches available:
master- the latest stable versions of CodeIgniter and Doctrine.
develop- the latest development versions of CodeIgniter and Doctrine. Not recommended for production use.
doctrine-2.1- the latest stable version of CodeIgniter, and the latest stable 2.1.X version of Doctrine. This branch is provided as a way of keeping Doctrine 2.1 applications up to date without breaking backwards compatibility.
For more information, read my post on integrating Doctrine 2 with CodeIgniter 2