Create an Action for a Trigger

Hi Experts,

I am an experienced PHP programmer but a litter bit new to Drupal.

I have created a new content type and set a trigger for a new post, but I don't know where to place the action scripts so that the trigger could be automatically handled. This content type is pretty simple, so I guess it may not be worth to write a module. I am not sure it's a normal way to deal with triggers and actions. Hope you experts could give me some hints, and any suggestions are welcomed. Thanks!

BTW, I'm using Drupal 6.4.

Cheers,
Steve