Not really!
All that you need to do is to switch on your modem .
Type ‘sudo pppoeconf’ in the terminal. Enter the root password and just keep selecting yes. At one point of time it’ll ask you for your Username and Password. Just ping that it and keep saying Yes. You then shouldn’t be having any issues with connectivity.

I’ve never used Kubuntu. It must be working on the same lines though.

Yes! You can get yourself hooked to the net even in Live cd mode.