I'd like to share my experience with setting the initial folder rights for some special folder with you:
Initially the public folder 'Global Address Book' had the rights set so that only every user could change his/her own entry. No administrator could change the entries for other users.
For our case this was not sufficient but there is no way to set the permissions via the GUI. So I had to add some entries manually in the database.
The table oxfolder_permissions contains the all folder permissions.
cid was always 1 in my case.
fuid contains the id of the folder which permissions you would like to shape.
permission_id is the id of the user or the group which the permission applies to.
The next for fields are for the 4 folder permission parts.
admin_flag is 1 or 0 - it sets whether the user should be able to control/change this very permission.
group_flag is 1 or 0 - it defines whether we are setting the permission for a user or a group.
You need to restart OX to make changes go live!
In order to find out the correct id for the folder and the user/group take a look at the tables oxfolder_tree and user.
Before you change anything make a backup of your database!