I'm really hoping there's an easy way to just install debian over my existing xubuntu installation. I don't want to deal with backing things up again, my external hard-disc is already almost full. I'm tired of continuously copying stuff, but I tried debian and like it way better than 'buntu. Is there any way I can simply make my ubuntu installation into debian but keep all my personal stuff?
Every Linux distribution is different in terms of how software is installed. Linux distributions use different installation file types, package managers, and commands for installation. Even within a single form of Linux, there are different types of package managers.
Y'know what else generates an /etc/fstab file for Debian is the Debian installation scripts. It may be a good idea to explain exactly why you're using another LiveCD to install Debian (since the ability to use that CD makes it clear that you can easily just, y'know, install Debian with a Debian installation disc or network image). But if that's really not an option