Only tested with the Debian 'woody' Samba 2.2.3a

Explaination of the security = configuration tag in smb.conf
security = SHARE : For clients w/o a valid user/pass 
                   combination on the server
security = USER  : For clients with a valid user/pass 
                   combination on the server
                   2 authentication mechanisms
                   encrypt passwords = Yes : This will use smbpasswd for main
                                             authentification.
                                             Supported platforms:
                                             linux, Win9x, Win2k(non,sp1,sp2)
                   encrypt passwords = No  : This will use PAM for main
                                             authentification.
                                             Supported platforms:
                                             linux, Win9x*, Win2k* (non, sp1)
                   non = no servicepack
                   sp1 = service pack 1
                   sp2 = service pack 2
                   * = With EnablePlainTextPassword set to 1 .reg file