Microsoft have a Genuine Windows program that offers a discounted way of getting a legal copy of a Windows OS. They will even let you re-authenticate the installed illegal copy with the new valid key (which even allows you to authorise a non-OEM install disk with an OEM COA key).
Get hold of an XP (just make sure you get the appropriate variant, Home or Professional) install, install it. Then, don’t enter the COA key. Windows will install, but give you 30 days to activate it. Then, from the activation tool, you can hit a link to the Genuine Advantage discount purchase. I know it works, because I just installed a Windows VM with the wrong XP disk (retail vs OEM), and could not use the OEM COA from the physical machine I had converted to Linux. I used the key change tool MS supplies rather than purchasing a new license, but I have purchased one from MS before, and it was cheaper than an OEM license.
Si