Setting up a Share Without Authentication
From SambaWiki
Anonymous Read-Only
The following /etc/samba/smb.conf file shows an example how to configure a read-only file share with guest access. Two directives are used to configure guest access – <map to guest = Bad user> and <guest account = nobody>.
[global] workgroup = SAMBA security = user map to guest = Bad user
[data] comment = Anonymous Samba Share path = /samba/anon_share read only = yes guest ok = yes