with XP you need to install the Multi Language Interface (MUI) pack, and set it up. It does take up a fair bit of space for each language (about 300Mb for Japanese if I remember correctly)
I used it while in Japan so all the visitors to the guesthouse could use the computers there, and it was pretty simple. Just created a bunch of users and associated each one with a language (and made pretty flag icons for the log in screen).
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You aren't thinking or really existing unless you're willing to risk even your own sanity in the judgment of your existence.
Green peppers, lime pickle and whole-grain mustard = best sandwich filling.