Hi Sharon,
I suspect you're seeing 1/1/1900 for the due dates because you're looking at the payment records, not the invoice records. Payments do not have due dates. You would have to link the payment to the apply records first, then link from the apply records to the invoices. I have actually done that in my code here: victoriayudin.com/.../sql-view-for-payables-payment-apply-detail-in-dynamics-gp. This code also includes records from the open tables, so if you have any partially applied records, it will capture them, as well.
Hope that helps.