So, what do you actually need? I'd recommend starting with at least B85. In my case I used the latest NexentaOS unstable release (1.0.1 to be) which includes B85 and by default the necessary Sun smb packages. For my test, I created a contrived domain using Windows 2003 Server (SP2) called WIN.NEXENTA.ORG. The rest follows:
add to /etc/resolv.conf:
(Nameserver is our AD DNS server)
(optional: run ntpdate against your time server)
#svcadm enable svc:/network/ntp:default
#svcadm enable -r smb/server
#smbadm join -u Administrator win.nexenta.org
#zfs set sharesmb=on data/myshare
#zfs set sharesmb=name=myshare data/myshare
#chown jlittle /data/myshare/jlittle
#idmap add 'winuser:*' 'unixuser:*'
#idmap add "wingroup:Domain Users' 'unixgroup:staff'
#svcadm restart smb/server
#svcadm restart idmap
Other advisable steps include "zfs set casesensitivity=mixed data/share" for correctness of Windows users, but likely not ideal if the zfs filesystem shared is also shared to NFS clients. You know if its all working if "idmap dump" gives you real values and not just returns to the prompt. I connected to my new share via a MacOSX client, and made sure my domain matched as "win.nexenta.org" when connecting to my share (aka smb://server/myshare/jlittle).
In the end, it was much simpler than the documents suggested. I had to avoid explicitly stating the domains in idmap to make idmap do the right thing. You should pick the right local group for your users in the mapping for groups. I picked "staff" as that was the default group of my user.