I have a really basic question; I just had cable modem service installed on my Red Hat 9 box and I don't have a host name or IP address assigned. Now when I log in, it says "Welcome to x17-x2-v23......." which appears to be my NIC's MAC address. It used to say "Welcome to localhost@localdomain". Questions: Do I now have to have a static IP address assigned? If not will DHCP work? I know this information should go in the hosts file, but what about a localhost@localdomain name? Do I need to create/invent one?
Any help here would be greatly appreciated.

You may have a stactic IP - that will be up to your ISP.

You can change your hostname to what you want with:
hostname myhost

You can also set it so it is retained after a reboot with:
HOSTNAME=myhost

in:
/etc/sysconfig/network

Whatever you set it to make sure it exists in /etc/hosts next to the loopback entry "127.0.0.1".