Normally, regional and language options-languages-details does the trick. There you can add any other language packet. Anything not installed will be prompted, then you put the XP CD and everything is OK. But if the package is not supported or not listed, then you may need a different version. I don't know any other method, but there might be another one.
Anyway, I didn't understand it at all, because US and UK keyboard are the same. They are both Q keyboards, and have the same keys on the board