As far as I know, you can't switch default calendars.
What you can do is add a new calendar which will appear side-by-side with your default calendar in the same window.
In Outlook, click File>New>Folder.
Give the calendar the name you want then select "Calendar Items" from the drop down menu in the "Folder Contains" box then click OK.
Next you'll have to map it to the new calendar's location.
Right click your new calendar and select properties.
Click the "Homepage" tab and use the "browse" button to the location of the new calendar, click OK.
When you open outlook today, click "Calendar" like you normally would. You will see the new calendar you created listed under "My Calendars". Click your new calendar and it will appear side-by-side with the default calendar. You can toggle between the two as well if you like.
The only drawback is that reminders only function in the default calendar.
Edited by HitSquad, 02 November 2006 - 03:21 PM.