The Order Number must be like this:

ORD0000

Thats "ORD" at the beginning followed by 4 numbers, I need to find the max existing Order Number and add 1 to this calculation as well.

So basically I need to know how to make a form automatically generate a new order number starting with ORD but I have to find the max and add 1 on to this to make it unique. Any ideas?