Net connection fail in the middle of upgrading, now what?

[Saturnina]

I was upgrading to 8.04 but at some point it got stuck and didn't progress or download anything anymore. When I rebooted, I could only access the failsafe mode and it could not connect to the net anymore. If I now download and burn the alternate cd, will it figure things out automatically if I run it in the failsafe mode, or is there something I should do before running it? Or is there a way to un-upgrade the partly upgraded system so that the net connection would start working again?

What should I do?