Ok, time to wrap this up. My error was that when virt-install first asked for network information, I gave it values that did not work at that time (values for another live machine that I meant to replace with the new virtual machine).
I did not realize, these values were only for the installation, not for the newly-created virtual guest.
After that, the installation from my own http "mirror" (over gigabit net) started ok. It is still running, about as fast as from an optical drive.
- Jussi