Any problems you see before restarting X are not going to be relevant. You need the nvidia drivers in use (both the kernel module and the X drivers) to be able to do anything; so any use prior to reloading X is going to not be using current info.
What you should be doing is rebuilding the NVIDIA_kernel package in X (if you really have to use X at all), editing your XF86Config file in advance, then installing the NVIDIA_kernel in text mode. Exit all the way out of X -- don't even let xdm/gdm/kdm/whatever be running. If they are, then do an init 3 as root in a shell to shut them all down.
Then install the NVIDIA_kernel RPM, followed by the NVIDIA_GLX one. Then make the changes to XF86Config (if you didn't before), and do a startx to test. If that fails, copy your /var/log/XFree86.0.log to somewhere else (like your home directory), undo the changes (here you'd have to use a text-mode editor) or just use Lynx, and attach that log file here.