How to convert from functions to templates

In Drupal 6 getting Drupal to recognize the theming hook as a template is automated. These are the only requirements to trigger this change:

• Name of the template must match the theming hook.
• The underscores in the hook must be changed to hyphens.
• The template name must have an extension of ".tpl.php". (It can vary based on the theme engine.)

However in Drupal 5 you need to call _phptemplate_callback() to force the override.

References: About overriding themable output