pam_ldap and nss_ldap are different packages. pam_ldap is for Pluggable Authentication Module architecture. It allows applications to be independent of auth method (Unix passwd, LDAP, etc.)
nss_ldap is for Name Service Switching which is used to tell OS what sources to use in order to access different system databases (passwd, hosts, groups, services, sendmail aliases, automount points, etc.)
If you use pure LDAP auth in your SAMBA you probably don't need to have pam_ldap on your box. But I'm not 100% sure, I have both of them cause it cists nothing. Try PADL documentation regarding this.
Are you going to have experiments on production system? :-)
The best approach from my point of view is
to have standalone test SAMBA server,
to configure it for different SAMBA NT domain and auth with LDAP,
to configure 1-2 clients for joining this test SAMBA NT domain.
smb.conf file should contain lines for LDAP authentication.
here is quite competent URL