With each customer record, you may setup to use a Blanket Purchase order. A blanket purchase order is used by schools or some other organizations that want to use the same P.O. for each order they place with you.

To setup a blanket P.O., simply open the customer record you wish to work with and click on the Misc. Customer Settings tab

Now check mark the Blanket Purchase Order box, enter the P.O. and date range.  This will cause all invoices created for this customer within the date range to be assigned to the P.O. # entered. 

In Addition, If a customer requires that a P.O. be assigned to all invoices, you can also check mark the Require Purchase Order to Direct Bill box.  This will cause BizWizard to require you to enter a P.O. # for all new orders.