project page - http://drupal.org/project/workflow
what does it do? - This module allows the creation of workflows to node types. Workflows are made up of workflow states. For example, a workflow with the states Draft, Review, and Published could be assigned to the Story node type. Actions can also be assigned to the transitions between workflow states. For example, an action could be assigned so that when the story moves from the Draft state to the Review state an email is sent out.