I picked a three DC (domain component) auth realm/domain at zeroshell profile. My domain looked like mydomain.com.ar (DC=mydomain, DC=com, DC=ar). With this configuration, a good host name is myhost.mydomain.com.ar
The installation script is checking for a 3 component hostname no matter the DC number in the domain of your choice (there is an if -complex parsing thing-==3). The installation is always waiting for a myhost.mydomain.com formated FQDN.
I was forced to change the internal auth realm of zeroshell in order to be able to install zerotruth. After creating a new profile with a 2 component FQDN, the installation works fine.