Hi,
dennisnoyes, and welcome to the forums.
In Office '07, I think you can use the following method to do it....
MS Office 2007 - Spell check in multiple languages - The Something Awful Forums
If you're referring to Office 2008 for Mac, I am not sure you can.
Also, here is another alternative - OpenOffice.org -
New ways to select language for spell check - OpenOffice.org Ninja