One way is to open a konsole and type: kdesu kwrite
enter root password when prompted. That will open kwrite with root permissions.
Then navigate to /etc/modprobe.d/sound and edit the file.
Another way is to open konqueror as a regular user, navigate to /etc/modprobe.d/sound, then right (or is it left ? ) click on the file, and select open with “other” (or something like that) and type: kdesu kwrite
and that will open the file with kwrite with root permissions.
My apologies for my vagueness … I am not on a Linux PC right now, and my memory is pathetic for these sorts of details.