choose which menu(s) appear in the "Parent item" select box in Drupal

When creating or editing node in Drupal, we have a field called "choose parent item".

In this one I just have one menu. I would like to control which menu to load in this selectbox?

I am using Drupal 6.

For Drupal 6 try the Menu Settings Per Content Type module. It will let you select which menus to use for your nodes from the content type edit page for each content type.

This feature has been incorporated into core for Drupal 7.