Microsoft setup a great guide for opening shared calendars from the various versions of the Microsoft Office suite.
Check it out here: http://support.microsoft.com/kb/912265
I recently shared an Outlook 2007 secondary calendar (not the default one) with a user who had Outlook 2003, and Microsoft’s guide didn’t tell me that I would need to adjust the sharing properties of the user’s default calendar (in order to provide access to drill-down to the other calendar..)
- Rt-click the user’s default calendar and select Change Sharing Permissions.
- Add the user who is going to be sharing
- Set Permission Level to Reviewer
- Under Read, change the radio to NONE (that way the 2003 user will not see the 2007 user default calendar…only the secondary one underneath it)