I have acquired an old PC, Don't know if it works or if its just good for parts, but it dose has an XP home key sticker on the case, is there any way to check if the product key is in use on another PC or if it is free to use?
Keep a note of it anyway and if you install XP on a PC try it. If it works and you activate then you have scored. It might well be a retail anyway. I myself see nothing wrong in using OEM on another machine, as far as I am concerned if I have bought the PC I have also bought the operating system and if I choose to move it to another PC then that is my business.
If it won't accept key or activate because it doesn't 'tally' with the manufacturers BIOS you usually have to ring MS and do a phone activation and tell them that you have had a motherboard failure so you have a new motherboard and also are installing on a new (bigger) harddrive. But then again it really depends on the make of the pc and how the OEM is set up. There are a lot of variables so it is not clearcut if it will be okay or not. Best way is to try it and see what messages come up.