After many fresh installations of Virtualmin GPL under - Debian 4.0 AND - CentOS 5 I find always this:
I'm using an external DNS.
I already have many domains pointing to this server.
After fresh installation of Virtualmin all of the above domains show just the default (empty, Error message) content.
After I create just one virtual server, ALL of the above domains now are showing the content of this single fresh created virtual server.
This behaviour is the same under Debian 4.0 and CentOS 5.