[Samba] Samba 3 with Unix passwd authentication?

[Andy Moran]

We are a primarily Linux company with a NIS backend, but we keep a 
couple "bridge boxes" for Windows users (on a Windows PDC) to connect to 
their unix accounts and access data.

Under Samba 2.2, this was fairly easy with "encrypt passwords = no" 
turned on.   But I can't figure out how to make it work with Samba 3. 
Does Samba 3 not support a unix passwd backend, or am I just missing a 
configuration option?

--Andy