Ubuntu 6.06.2 LTS (Dapper Drake)
Make sure you get the server version.
My instructions assume that you have another box running as DNS. I'm not sure how to make the zimbra box act as a DNS.
You don't have to have a separate server running DNS, it can be on the Zimbra server as shown in most of the wiki articles. That's done for convenience (and that DNS server is used only by the Zimbra server) and for users that don't want it on a second server although you can, obviously, have a DNS server located anywhere you like on the LAN.