Copying new records

Hi

I need to copy new records from an access table which can potentially have
records added to it all the time by users. I figure I can add a flag for
records that have been copied already that can be set after copy. The
problem is that in the time that I copy all new records using 'select * from
... where not flag' and coming back to update flags for all records not
already flagged, new records could have been entered by the users which may
also get flagged as copied with 'update ... set flag=true where not flag'.
How can I differentiate between the records that are copied and still not
flagged and the records that are new and have not been copied.

Thanks

Regards