I've never heard of Samba authenticating off NIS, as Windows (SMB/CIFS) and Unix (PAM, NIS, etc) use different incompatible password hashes. on a pure Samba system that doesn't have an external authentication system such as Active Directory, I've always had to use smbpasswd to setup the SMB passwords for the 'windows' users.
Yeah, this is what I'm afraid of - that I'll have to install some directory services.
I'm going to start off next week with a call to Oracle. Just figured I'd ping the list to see if maybe someone had been here.