Outlook 2000 or 2003

Can the booking of "All Day Events" in a resource Calendar be disabled? Due
to the fact that All Day Events show as Free and not Busy mean we're having
quite a few issues with duplicate booking.

We do know the correct process of booking a meeting by creating a new
meeting and adding the resource as a resource in the invitation list, but as
always users tend to do things their own way go directly to the Calendar of
the resource.