Selection of Language

At IPA, we need to be able to write in US English or UK English depending on which client we were preparing material for. in XP/Office03 I found this easy with toools-language.

But I can't find how to do the same here - I think I've set every to UK English in control panel and in File-option-language, but it's still telling me I've spelt organisation incorrectly when writing in "UK"

I believe our Office 13/Windows 7 laptops have been set up to default to US English.

Please tell me how I can set up Word/Powerpoint etc to easily switch between the two languages

Thanks so much