My original problem is listedbelow

I am using Data Validation for selected vehicles on runs, but I need to stop
people assigning a duplicate registration for seperate runs.
The list for the data validation is in cells D91 to D120 and the entries are
made in cells H3 to H47

ALSO - on the same sheet I need to stop people using the vehicle
Registrations from the validation in cells H48 to H60 - can I use the same
validation list or do I have to set it up again

I have used all the info from http://www.contextures.com/xlDataVal03.html to
sucessfully create a dropdown that doesn't show a duplicate entry, but i need
to allow the users to be able to manually enter a registration, but stop them
if it matches one of the entries within the data array - is this possible??