Have you looked at the Menu Per Role module (http://drupal.org/project/menu_per_role)?  Unfortunately it only exists for D5, but it works for me.

Steve

Daniel Carrera wrote: 
Hello,

Is it possible to make a menu entry visible only to authenticated users?

Ultimately, what I want is to replace the "create content" page by a 
custom page, but naturally, I only want that link to be visible to 
authenticated users, otherwise I'll just confuse the other users.

Daniel.