need to edit system files, don't know how

[hoyeru]

I need to edit these two files:

/etc/network/interfaces and
/etc/rc.local
because my PPPoe connection won't stay up but for just a few seconds.
I tried doing it in KDE with Konqueror but got the message that i cannot edit and save the edited files. What can I do now, do i have to do it with the command line?
If command line how do i accomplish that?

[penguin.ch]

Re: need to edit system files, don't know how

One way (of several possible): launch an editor "in root mode", e.g. by [Alt][F2] kdesu kwrite and proceed from there.