shared calendars

We are running Exchange 2007, with Outlook 2010 as clients. 

We have several shared calendars, but I can't seem to located them / access them in Outlook 2010.  When I Click on Open Calendar and the Open Shared Calendar, none of the shared calendars show up in the list.  When I search for a specific calendar by name, it can't find it....

any help / insight would be appreciated.

thanks.