the concept would be the same as in this thread, only the opsite:
showthread.php?t=15535
in that thread, they are trying to make sure the value is not in the database, so the numeric validation uses a minimum of -1 and a max of 0 to make sure the recordset is empty.
Use the same idea, but use a minimum of 1 and max of 100, this way validation will pass only if the value does exist in the database.