How To Append Multiple Rows Using Append Qry?

I´m trying to improve my appl. but I´m stuck trying to figure out how to append multiple rows on a table using the Append query.

My problem comes since I have 4 tables with the following fields:
1) Orders
OrderID (number)
CustomerID (number)
Date (date)
etc...
2) OrderDetails
OrderDetailID (number)
OrderID (number)
ProductID (number)
QuantitySold
UnitPrice
etc...
3) TmpOrders
OrderTmpID (Autonumber)
CustomerID (number)
Date
etc...
4) TmpOrderDetails
OrderDetailTmpID (Autonumber)
OrderID (number)
ProductID
QuantitySold
etc...

The problem comes since the Tmp tables are used just to record temporarly the information before the transaction is completed.
Whe the salesman at the desk finish the sale, a command button is presseed and an append query runs to transfer the data from Tmp tables to the Definitive tables. Another query (Delete) is excuuted inmediately after the append qry. and it deletes the information recorded on Tmp tables.

I need to reset the autonumber or create a field that records the line number so I can add up to the Maximum OrderDetailID found on the definitive table, but the problem is how to create the "controlled" autonumber.

Please help.