I'm not sure why there are such things as locked menu items in Drupal 5 in the first place, but there are. And we'll have to deal with them.
My most recent head scratcher: how to hide a locked menu item, like "my account" when you have no way of editing it? The workaround proved to be diabolically clever in all its simplicity:
* create a new menu (_dummy_ in my case)
* create a new menu item under _dummy_ and point it to the locked item's url (_user_ in my case)
Result: the item is automatically moved from _navigation_ to _dummy_ and since nobody has access to the new menu by default, _dummy_ is not shown.
Though this hack is quite straightforward, it shouldn't be necessary in an Ã¼berflexible framework like Drupal.