We followed Gregs Tutorial with a bit of success and are able to authenticate against Zimbra.
We're now trying to join machines to the domain but are coming undone around about....
"Next, create “Domain Admins” group using Zimbra Admin UI, on Samba tab select Special Windows group type “Domain Admins”."
We don't have domain admins available on our Posix Accounts Zimlet. I'm not sure which step we stuffed up, probably importing the samba.schema file from 3.0.28 but if anyone could let us know which part of the process creates this "Samba Group" option for posix accounts it would be most helpful.