Booking Conference Rooms

We are having trouble with people double booking conference rooms. When
one meeting is an all day event, lasting 1 to 3 days, someone else can book a
meeting in the middle of that time. Sometimes the second booker says the
could not see the first meeting. All of these meetings are booking the room
as a recource.
I am wondering if the fact that we use 2003 and 2007 makes a diffrence?
Or is there a diffrent reason that this happens?