To hide all drop zones on a menu screen:
Make sure the menu whose drop zones you want to hide is showing in the iDVD window.
With your pointer over the menu, press Command-I to open the Menu Info window.
Deselect the “Show drop zones and related graphics” checkbox.
The drop zones immediately disappear from the menu, and they do not appear in your final burned project. Some other graphical elements may also be hidden.