You must edit /etc/inittab as root since it is the only one that can write to it.
Once done, reboot and see that you go to text mode, log in as root, find your installer and run it. If it succeeds, you can then type:
to go back to graphic mode... however before you do there is something else to change. Check the nVidia readme to see that you need to edit the file:
to make the new kernel module work. As a linux noob a year and a half ago, I found the RedHat Bible series books to be very helpful, so I suggest you grab a good book, really.