Software

First you will need to activate the languages you want in XP from Regional Settings in the Control panel. Select the lanuages you require and you will need to reboot (and have your orginal CDs handy as well).

After the reboot open Office (for example Word), open Tools menu on toolbar, select 'Set Language' and you can select the languages you require and also set the default language to activate the dictionary you require. Don't forget to set the language in Outlook (or Oultlook Express) as well - Tools menu, then Options, Spelling tab and so on.

If you find that Office does not keep your default language setting then you need to reset the Default Language in Regional Settings in the Control Panel the language of your preference even if it is not the region you are in.