A second look revealed that the isolinux.cfg file was actually in the folder /media/DRIVE/isolinux, and that I needed to move this file to the root and rename it, which I have done...

now I've followed the steps, and also realize that the second part of the last step last time: how does one set the boot flag with fdisk? I'm looking it up, and it seems that it's with the -flag option, but I have no idea how to use fdisk at all, or even what that program is useful for.

L