First lets take a look at why this happened to you. When you connected to this network you got an IP from their DHCP server, but in addition to that you also got sent a hostname to use.
In a file called
ifcfg-eth0 (usually found in /etc/sysconfig/network directory) you have a line saying something about
USEPEERDNS = Yes, this is what made your hostname change. Setting this to No would have made your linux ignore that hostname info from the DHCP.
I don't know exactly which file is making trouble for you here and now. You should not have to add the plwstellantvivare.com hostname in your hosts file. In this situation I would search the files in the /etc directory for instances of that hostname. As root user run the following command to do that.
Code:
grep -r 'vivare\.com' /etc/*
This would show any lines that contain the word vivare.com along with what file it is in.
Post your findings here.