[OT] Help with windows activation

[Mike Bonner]

Hey all, hope its ok for me to pick everyones brain..

I am working on a system for a friend. The previous person "helped" them by
installing vista ultimate for which they have no valid license.  Didn't
activate it, 30 days later everything goes wonky.

They do have a valid vista license, just not for vista ultimate.
Unfortunately windows activation won't accept the code because of course
its for the wrong vista level. Does anyone know of a way to downgrade from
ultimate to home premium so that I can then activate and not have to do a
reload?