If you are using a version Microsoft Outlook older than Outlook 2007, the holidays available for your Calendar folder will expire at the end of 2008.
However, Microsoft offers updates for previous versions of Outlook to supply holidays for tupcoming years. For Microsoft Outlook 2002 and earlier, the update provides holidays for the years 2006 through 2012. For Outlook 2003, the update supplies holidays for the years 2007 through 2012.
For Outlook 2003 users, you can download the update for your calendar here: http://www.microsoft.com/downloads/details.aspx?FamilyId=32C24709-50B5-4698-B5CB-BE7D6765FE3A&displaylang=en
For Outlook 2002 users, you can download the update for your calendar here: http://www.microsoft.com/downloads/details.aspx?FamilyId=EA8DF27B-3130-47AA-AB09-E99F4BE721A5&displaylang=en
For Outlook 2000/98/97 users, use the update listed for Outlook 2002 users. Upon download, save the file as a .txt file, instead of .hol. This is because the holiday file was only named .hol starting with Outlook 2002; previous versions use .txt.
Microsoft Exchange Server: