Track when the value in a column changes

Hi
I have a MS Access 97 database. New records are inserted and existing records are updated by applications that I have no control over.
I am interested in one specific column (time_stamp) in a specific table (event).
I want to know when the value in the timestamp column is updated. As soon as this happens I want to run a macro. The column may be updated thosands of times a day.
Thanx and Regards.
loubu01