Re: Kubuntu and build-essential
So if I understand correctly: You can install a certain package from a Live session w/o internet but not from your installed Kubuntu?
Maybe the live session has the DVD itself listed as a package source and the installed Kubuntu hasn't. You could try to add the DVD to the sources in Muon Package Manager. See settings > configure software sources and then the tab "Other Software". For me the CD (I installed from CD) is unchecked there by default.
"I believe humans get a lot done, not because we're smart, but because we have thumbs so we can make coffee." --Flash Rosenberg