John's method will limit the VALUE of a PK, but not the number of records.
For example, if you have records with PK's of 1-100 and delete 50 of them,
you still won't be able to enter any new records because the next one will
get a PK > 100.
Another way: In the BeforeInsert event of the form that inputs new
records, check the DCount for the table and cancel the insert if
DCount=100. However, events only work in forms, not in tables. Thus if the
user can open the table directly, records can be inserted without firing
the BeforeInsert event.
-TedMi