Although some think there's always a EULA violation, here's Microsoft's total take on the subject: Downgrade Rights Details and FAQ

 

downgrade rights depends upon what version of vista it is. You can only have downgrade rights for vista ultimate and business. What version of vista was on the sticker?

How do I downgrade? Install a copy of Windows XP Professional with the product key that came with the copy, and then when you hit the activation screen -- which is near the end of the installation process -- select the activate by phone option rather than the online method. You'll likely end up talking with a live rep; tell him that you're downgrading from Vista to XP, and give him the Vista product key. The rep is supposed to walk you through the rest.

FAQ: Giving up on Vista? Here's how to downgrade to XP - Computerworld

 

Thank you , sobeit.
I'm relieved there might be a totally legit way to activate XP Pro on these machines. At this point there are two and the wording on both stickers is "Windows Vista Business OEMAct. Any resources you can point me towards to activate would be greatly appreciated.

 

the link in my other posts tells you exactly what must be done to downgrade.

 

Missed that, thanks.