One simple thing you can consider is setting the "correct" language in Word and running spell check. There is a choice between US or UK English there, and when set in Word the setting is applied to all other Microsoft Office programs. When you set a new language, spellcheck should switch automatically to using the appropriate dictionary. As there's lots of crossbreeding/inbreeding between the languages, I can't say how strictly the associated dictionaries will distinguish between the two languages.

You may have to reinsert your installation disk the first time you change to a new language, but once installed the language choice should choose the appropriate dictionary for the spell check.

Note that there is some difference in keyboards as well, and you may find things "in the wrong place" if you don't switch back to the language that matches your keyboard.

In Word, "Tools|Language|Set Language."

There are a number of other things that can be set to be more appropriate to the particular language, with the most basic entries at "Options," some additional possibly at "Customize," and likely some in "AutoCorrect."

A "sort of" definitive reference is Developing International Software, Second Edition
Author: Dr. International   
Pages: 1104
Disk: 1 Companion CD
Level: All Levels
Published 10/09/2002
ISBN 0-7356-1583-7

(For those who might look at the link, it's to http;//thesource.ofallevil.com - and it is a Microsoft site. Links to discount sellers are provided for this book [not exactly a best seller].)

I doubt this book would be of a great lot of help in your task, since it does deal primarily with software, but the really desparate might find some help with getting the software they might need for using some of the features available in standard Windows/Office.

John