1) Except Redhat and some who change the default locations of files and default attributes, most distros follow the traditional structure. For Debian, I guess it's id:1:initdefault for text login.
You must take a look at the look of every conf file. You can't blindingly change things.
2) It's not on Gnome or KDE control center because it was installed there. Simple as that. You could look at their Website for answers.
In full circle: you could find out what starts your graphical login from /etc/inittab's "script to run going to other runlevels". Mine is:
l5:5:wait:/etc/rc.d/rc.sysvinit # X window and xdm
Open that file up. It'll lead to another file. And another. And another. You'll find the right file eventually. It'd be good to know what graphical login you're using. gdm or kdm or xdm?
3) That's odd. Your BIOS may use the key combo for power down. Check it out. Disable it.