NFS has the ability to "root squash" or "all squash" - map authenticated users to alternate user ids, for purposes of security. This makes it easy to setup an NFS public folder where all users share the same permissions.
Samba on the other hand, does not have such capabilities. However, you can achieve similar functionality by configuring a "guest" user, which maps to a specific local user id on the server.
Simply open /etc/samba/smb.conf and enable the following line:
guest account = [mapped user id]
That's all there is to it! Now any anonymous client can access the shared folders, and they will automatically have the same access rights as if they were logged into the server locally, with the username specified in the smb.conf file.