[development] User registration email

A client I am working for asked to have a special landing page set up for user registration for an event. The registration form uses user_register to create a Drupal account (using Drupal 6). Form works great, creates account and logs people in upon account creation. How do I go about creating and sending a custom email that includes the new account username and auto-generated password? Do I need to create my own user_register_submit function to override the current (seems redundant) or is there a simpler way? Jeff