One new feature of Drupal 7 is that any title you give a node will be copied to the menu title field when you create a menu item. I wanted to replicate this functionality in Drupal 6 and so I created a function that did just that. I have used this function a few times in different projects so I'm posting it here.
This code also does a small amount of validation to encourage users from adding massive menu titles by adding an "error" class to the field if they add a long title. This is currently set to 80 characters, which seems like a good limit.
To use this function just add it to one of your own custom modules or even create a module for it.
You could possibly do it via a hook_form_alter on the form and include the drupal_add_js() call in a form #after_build callback.