The only way that I know of to do this is through Outlook.
You can log in as administrator to a desktop or server that has Outlook installed
From Outlook, right click public folders and choose new folder, type a name. On the “folder Contains” drop down, choose Calendar Items.
This is great if you have the ability to log into a machine with Outlook which is not always the case, there is a workaround.
By default, only administrator have permissions to create new public folders, this is for good reason and should be left this way. From Exchange 2007’s GUI, you can navigate to tools>public folder management (SP1 and up only.)
From here, you can create a new public folder.
Once the folder is created, you can use pfdavadmin to give the user or group permission to the folder.
Once the user has permission to create items in the new folder, they can right click it and choose new and setup their own public calendar.