If you are not on an Exchange Server, more than likely none of this applies.

What happens when you select File, Open, Other User's Folder, then enter in
their username and select Calendar as the Folder Type?  If they gave you any
permission at all, you should be able to open their calendar this way.

However, if you want to add them to your Folder List, they have to give you
permission both at the Mailbox level and the Calendar level before you'll be
able to do that.  (Most people will set you up at the Calendar level, but
forget about the Mailbox level).  If you think about the mailbox level as
being a locked drawer in a file cabinet and the Calendar as being a folder
contained in that locked drawer, someone has to give you the key to unlock
the drawer before you can see any of the files that are contained inside of
it.

Good luck!

tbgg
TrueBlueGeekGirl