I've figured this out now :D:D. [PNOSEQ] is the PK in TblPurchaseOrderData....
SELECT TblAddress.PUAddress, TblAddress.VendorCd, TblTblAddress.Active
FROM TblAddress
WHERE (((TblAddress.VendorCd)=DLookUp("[PNSUPP]","[TblPurchaseOrderData]","[PNOSEQ] = 1")) AND ((TblAddress.Active)=True));