The feature you really need to use is Delegate Access - a user grants another user a certain set of permissions to one of the default folders in their Mailbox. For calendars, that's the normal way of letting non-organizers make changes to an appointment.
When you are using a Public Folder, then it's folder permissions that grant varying levels of access to specified users/groups. However, I'm not sure if non-organizers can edit appointments in that folder even if they have the rights.
If you simply want to approve the creation of items in a Public Folder, then use the Moderated Folder features for that folder (I think it has to be mail-enabled).
http://office.microsoft.com/en-us/outlook-help/create-and-share-a-public-folder-HA010148803.aspx
Eric Legault
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