Bad news: the calendar in Outlook 2007 doesn't display holidays, unlike previous versions of Outlook.
Good news: adding holidays to your calendar is easy! Just follow these steps...

1. 1. Open Outlook
   2. Click Tools on the menu bar
   3. In the Tools dropdown menu, click Options
   4. In the Options dialog box, click the Calendar Options button
   5. In the Calendar Options dialog box, click the Add Holidays button
   6. In the Add Holidays to Calendar dialog box, click the box next to United States, and then click the OK button
   7. The Import Holidays window will open
   8. When a "The Holidas were added to your Calendar" confirmation dialog box pops up, click the OK button to close it
   9. Click the OK button to close the Calendar Options dialog box
   10. Click the OK button to close the Options dialog box