Tnx. a lot for your help.
Your solution did not work at all.
However I found the reasson why it didn't and will write for future users reference.
After Ubuntu is completely installed and upgraded and there are no blocked ports in the router, one must change the DHCP to static, and write the new domain name (ie. myserver.com) then you "echo the system tu use the new domain name, so..., to connect with SSH with the other computer, in a console one must write:
Thanks a lot for your help and
Luis C. Suárez
PS1. The steps above must be done after ssh and ssh-server is installed in the ubuntu box.
ps2. None of the methods like: 192.168.0.1 or 192.168.0.100 worked at all. I did not tried 192.168.0.255 however