There's a lot of steps to make this work. Sadly NT 4.0 has fallen out of support. There's also that nasty exploit (bug in NT 4.0) that never was patched. I'm a bit surprised when I find NT 4.0 still running.
Try the older NT and NTLM settings noted at:
http://www.enterprisenetworkingplanet.com/windows/article.php/3849061/Use-Samba-With-Windows-7-Clients.htm
Bob

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