MS Office 2007/2008 Proofing Tools
Microsoft will (presumably) keep adding to the list of languages for which they provide proofing tools. You can find one such list here.
They also have a chart of the available features for each language.
Using Proofing Tools in Windows
Select all of the text by using the keyboard shortcut Ctrl A or by clicking on Select in the far right of the Home section of the Ribbon. Set the language by going to the Review section of the Ribbon. Click on the Set Language icon, then click on the desired language and click OK. Note: If the desired language is not available, you may need to install the proofing tools. If this is the case, you will need the original install CD.
Once the language is set, click the Spelling and Grammar icon on the far left of the Review section of the Ribbon to use the proofing tools.
Using Proofing Tools on a Mac
Select all of the text by using the keyboard shortcut Cmd A or going to Edit > Select All. Then set the language by going to Tools > Language.
Click on the desired language and then click OK.
Once the language is set, go to Tools > Spelling and Grammar to use the proofing tools.