Add a subdomain name to Virtualmin
Login into the admin panel.
There are two ways to create subdomains. The way I prefer is this:
Click on "Create Virtual Server"
Select "Sub-server" as the type of virtual server on the top links.
In domain name, type the full domain name (without http://) but including the primary domain. For example: node.chatzone.tv
You will then get a new folder as the www root :
Et voilà !
If you want to run node.js on it, read my post about Running Node.js applicaiton with Virtualmin.