>In the record validation rule for the table I do something like this
>

IF EMPTY(TheMainKeyField)
>  USE (DBF()) AGAIN IN 0 ALIAS AutoNumber ORDER TheMainKeyIndex
>  GOTO BOTTOM IN AutoNumber
>  REPLACE TheMainKeyField WITH AutoNumber.TheMainKeyField+1
>  USE IN AutoNumber
>ENDIF

Bear in mind that this won't work in a multi-user situation, where two users might grab that record at the same time. The separate table for keys works better here.