You don't need to edit /etc/inittab, if you all you want to do is install the Nvidia drivers. Simply hit <ctrl><alt><f2> (or f3, f4) and login as root and run 'init 3'.
Once all the messages stop, just hit enter and do whatever you need to in the console mode. Install the driver, etc.
Once done run 'init 5'. No reboots are needed.
There are different editors depending what you are doing. If you are using console you can try 'nano', 'vim' or 'emacs'. If you are in gui there are many more. Try 'gedit', 'kate', 'nedit', or any text editor you see in the menu. All should work.