If you're going to upgrade to 5.3 (which you should!), I would highly recommend Doctrine 2 (not 1, very different project). It's a loose port of Hibernate from Java and takes a very different tack then most PHP ORMs. The models have no mandatory base class, the pattern is more Data Mapper then Active Record, it allows batch flushing to the database, has associations, and has some really great features like inheritance mapping and an event hook system.

There are pieces to dislike (arguably DQL, soft deletes are almost impossible, etc) but so far, it's a huge step forward from the likes of Zend_Db_Table or Doctrine 1.

http://www.doctrine-project.org/projects/orm/2.0/docs/refere...