Are you saying you used a "lookup" data type in your table? This may cause
you headaches later on, especially if your ZIPCode table uses a primary key,
and your Contact table is storing the key, but displaying the ZIPCode.

Rather than working directly in the table, consider using a form to display
information. Build a combo box on the form that uses the ZIPCode table as a
row source, and is bound to the Contact table ZIPCode field. You would need
to change the "lookup" datatype to an appropriate different type.

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Good luck

Jeff Boyce
Access MVP