Not knowing what the person buying these machines are going to do with the machine I would put a linux version on it. they are all free except Lindows which sucks. I have sold some machines with Red Hat and the owners have been very happy with it. I might add that, how are you going to make any money building machines anymore, the support is going to kill you believe me. If you put a unlicienced OS on and the customer is unable to get you to fix it right away they will blame it on the OS and call MS and raise hell, big trouble for you.
Bleep