"Why would they work fine 4 or 5 times, then suddenly get weird on me?" you
have to clarify if it is the network, the number of isos, the iso that shows
up a prompt,...
About the network.
ifup/ifdown only works if you have a configuration file
(/etc/network/interfaces by default) that has definitions for the network
device you use has argument. I know the eth0 inter face exists, because
otherwise you would get a message about the device not existing from ifup. So
you have to make the choice of either configuring the file manually and using
ifup/ifdown or using a GUI/console-interactive program.
You will have to be more clear where exactly you got the prompt is it
immediately before the install/boot live cd menu or afterwards? Did you
change any of the default boot flags on this menu? Things like that will
help. If you can access any logs that would help too.
