Two Tables in one form?

I have a admin ID from the admin table and a customer ID from the customer table.The admin requires a customer ID to link records together.  Once the customer is created I want a admin assigned to it. Or added.  One can only add a customer if it is a new customer, so I am thinking of some sort of way to allow this only when needed.  Any ideas on how to do this?  My thought process is some sort of registration key from a reg table. But my first problem is adding a new customer and a admin and assigning the just created customer id the the just created admin.