This page holds links to documentation about the module "heartbeat" for drupal 6. From here you will find how to install the module, how to use it and how to implement its hooks. As many drupal contributes, heartbeat comes with an export for messages that can be pasted in a hook function.
Heartbeat highly depends on the rules module. Rules allows other modules to describe default rules, and that's what heartbeat does. The messages you build are exportable into default as well.