If you work in Outlook most of the day, you may need to navigate from the Mail view to the Calendar, then to Contacts, and then back to Mail. Juggling those aspects of Outlook can be awkward.
Instead, try this simple tip to open Mail, Calendar, Contacts & Tasks in separate windows, it works in Outlook 2003, 2007, and 2010:
Just follow the directions at the How-To Geek's article Open Different Outlook Features in Separate Windows to Improve Productivity to find how this tip can make it easier to access your Mail and Calendar (or Contacts or Tasks) at the same time.