1. Create .HOL file & then import Holidays inside of Outlook

See Adding Holidays to Your Outlook Calendar
http://blogs.office.com/b/microsoft-outlook/archive/2008/01/18/adding-holidays-to-your-outlook-calendar.aspx

2. Download busyholiday.txt file
3. Rename busyholiday.txt to busyholiday.vbs
4. Execute busyholiday.vbs to convert all Holidays from free time to busy