[support] Dynamically display menu items?

Hello all, Let's i want to display or not display a menu item depending on some property of the logged in user. E.g. when my user has selected a project (i.e. a reference to the project can be found through the user) i want to display a menu item "my project", if not i want to display a different menu item "available projects". How do i do this? Context? Rules? Menu hooks? Any ideas? Best, Toon