When I start linuxconf and add an eth0:0, exit and activate the changes, it
works fine. ifconfig reflects the change.
When I start linuxconf a second time, the information doesn't get shown to
me, even though it's in /etc/sysconfig/network-scripts/ifcfg-eth0:0.
LinuxConf doesn't treat IP aliases as real network adapters. Look under
Config/Networking/Server tasks/"IP aliases for virtual hosts", and your aliases
should be there.