linking tables in access

Using Access 2000 frontend, SQL2000 backend. Have a need to delete and link tables based on criteria in a query. Example CustomerTableA has data about one set of customers. CustomerTableB has data about another set of customers. SalesTable has sales information about customers and, which table they are in, from both. When looking up customer information using the unique key in the SalesTable, I need to link up to the appropriate CustomerTableA/B. Merging the tables is out of the question because of the large number of records. I already have a script that allows me to delete the table alias that is already linked and bring in the other table using a form. Any Help Please.