Hi
maybe too late, but anyway :
I would like to use mydomain.org @ my LAN, but have subdomains, such as www.mydomain.org someplace else @ the Internet.
HowTo set up DNS with Zentyal?
I presume mydomain.org is already resolvable on the internet, maybe at your registrar or at your web-host level. That's fine...
For your lan, using Zentyal, you only have to create a dns zone for mydomain.org. Define all the LOCAL hosts you need in this zone (manually or thru dyndns on dhcp). This will only be used by your lan hosts/servers to resolve.
Make sure every machine in your lan can resolve this "local" mydomain.org.
Then you only have to add a record for "www" in "mydomain.org" zone and make it point to your webserver's ip address. That's it!