Alexander Netkachev has posted this quick tutorial with a few examples he's made for extending the Zend_Db_Table class from the Zend Framework.

He sets up the situation (complete with database table) and explains the creations of a "Users" extension to the Zend_Db_Table class. He shows how to set it up to work with your table name, and how to create a new user with the sample table provided.

He also demonstrates a simple validation wrapper around the functionality just to ensure that invalid data isn't passed in.