At work we have a Windows XP computer that is used mainly to test websites in Internet Explorer to check the stylesheet compatability. The installed XP version is English and everything is therefore in English; except one thing.
Surely this is a bug. The reason why the deviating language is Swedish and not French or Icelandic is probably because the MS Office 2003 we have installed on it is Swedish. I already had a Swedish Office CD from Sweden from before and at the time we installed it we thought it would suffice because we didn't want to buy a new English version for a computer we very rarely use.
PS. If you haven't already done so, migrate away from M$ Office and move up to Open Office which is free and Open Source.