Older versions of Outlook are "missing" holidays for 2008 and beyond. Microsoft has released updates for some versions and I converted the file to support older versions... see http://www.outlook-tips.net/howto/missinghol.htm for the files.

To use the updated holiday file, replace the existing holiday file found in the 4-digit language folder under C:\Program Files\Microsoft Office\Officexx, where xx is your Office version. For example, in the US version of Office 2007 it is at C:\Program Files\Microsoft Office\Office12\1033.

Then go to Tools, Options, Calendar options, Add Holidays and install the holidays.