Here is a guide to install the nvidia driver for your video card on Ubuntu 13.04, you can install the driver using the “Ubuntu-X” team PPA to your system.
To add the PPA and install the driver open a terminal window (press Ctrl+Alt+T) and copy+paste the following lines:
sudo add-apt-repository ppa:ubuntu-x-swat/x-updates -y
sudo apt-get update && sudo apt-get install nvidia-current -y
When the installation is finished you can close the terminal window.