Have you installed a driver for your card yet?
nvidia-xconfig: command not found
This would lead me to believe you are missing package(s). I do not run Ubuntu, so I can only suggest you go into Synaptic and look for the drivers and any util-nvidia package(s).
You might get some help from this tutorial.
Read the entire How To before proceeding.
It is also possible to install the driver from Nvidia. They provide complete binary packages for linux for most of their cards. That said, distros like Ubuntu usually discourage this practice.