I have a Windows XP Professional SP1 system with an illegal key (not mine).
I need to get it to SP3 in order for it to handle the software I am trying to install; I have a valid key for Windows XP Professional with SP3.
I seem to remember having a problem with this once before, like the key for a higher SP3 version not working to activate an SP1 Windows.
What steps should I take so that the computer can upgrade to SP3 with the new valid key without formatting it, or screwing it up?
A good answer would show a definitive activation and upgrade path that is sure to work, as making the machine inoperable is not a risk I can take.