I've had this same problem for ages. Maybe someone can help...
I have this graphics card: nvidia GeForce 9800b GT.
I've done this to install drivers: http://linuxg.net/how-to-install-nvi...-12-04-by-ppa/ .
I go to the nvidia system settings and I get this message: "You do not appear to using the NVIDIA X driver. Please edit your X configuration file (just run 'nvidia-xconfig' as root), and restart the X server." I do this and try the settings thing again, but I get the same message.
It's frustrating. I have this big monitor, but there's a big black border around my screen, and the resolution is much lower than the monitor is capable of.
I searched and found a similar problem from five years ago (http://ubuntuforums.org/showthread.php?t=993652) but I don't think the poster's problem was resolved.
I hope someone can help.
Thanks in advance.