Opening balances are simply loaded as a journal via GL_INTERFACE table. Adjusting period has no play here.
If you are bringing historical data from JAN-10 then make sure you make DEC-09 as your first period in GL. (You cannot do translation in your first period that is why always keep 1 spare period in the beginning).
You do not bring opening balancing from AP and AR. You simply bring open transactions if need be. However you need to make sure you remove the open AP and AR transaction's from your GL open balances to prevent double counting.