At login, just type "root" as your user name. But working as root isn't neccecarily desireable. I would recommend using a command line text editor as root.
You can use any command line editor, such as pico, vi, or emacs (to name a few) to edit these files.
^^^ that is a good vim command list. All you need to know, though, is:
press "esc" and then press ":" to execute a command. To get back into edit mode, press "Insert"
:P good luck!