pam_smb is a Pluggable Authentication Module (PAM) for UNIX systems which support the pam featureset. It allows authentication of UNIX users against SMB servers specifically (Windows NT and Samba servers, but also 95 or 98).
The Linux-PAM website is a good source of PAM related information. It is at http://www.kernel.org/pub/linux/libs/pam/
Pam_smb was written by Dave Airlie, at the University of Limerick in Ireland. His e-mail address is airlied@samba.org. pam_smb is now available on sourceforge as a project. A number of other developers have joined the project and are actively contributing. The sourceforge project name is pamsmb.
http://sourceforge.net/projects/pamsmb/
pam_smb is available on any site that mirrors the samba software, the primary ftp site being
ftp://ftp.samba.org/pub/pam_smb/
pam_ntdom is a modified version of pam_smb, created by Luke Kenneth Casson Leighton lkcl@samba.org, that uses the Samba NT Domain Security code to do the authentication rather than using the SMB calls. It can only be used to authenticate against a PDC or BDC, (NT or Samba).
Winbind is part of Samba and provides an NSS and PAM layer for UNIX systems, this means a UNIX machine can join an NT domain and get the user infomation from the domain, as opposed to with pam_smb where user information is still needed locally.