If you already have Exchange Server 2007 powerpack you can use this powerpack to manage Public Folders through PowerGUI.
This power pack will allow you to add/remove client permissions from Exchange 2007 public folders
On the ADD client you will have to populate the AccessRights= (example=author) and you will have to populate the User field
On the Remove client you will have to populate the same fields above to remove the desired client permissions.
Read more at source: http://www.powergui.org/entry.jspa?externalID=1959&categoryID=21