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