If you cannot install the driver in System > Administration > Hardware Driver, you should install the driver manually.
Visit http://www.nvidia.com/ and download the driver from NVIDIA.
Basically, NVIDIA provides the driver named like this:
nvidia-linux-x86-xxx.xx.xx.pkgx.run (older version)
nvidia-linux-x86-xxx.xx.run (new version)
nvidia-linux-x86_64-xxx.xx.run (64-bit system new version)
The “x” are some numeric value for the version (excludes linux and x86)

First, download the driver and I suggest you download it to your home directory.
Then, if you login and opened X Window System, you should logout and after logout the system, you should press Ctrl + Alt + F1 change to command line mode.
Next, you should type

sudo service gdm stop

or

sudo /etc/init.d/gdm stop

to turn off the X11.
Fourth, type

sudo ./NVIDIA-Linux-x86-xxx.xx.run

if you are at your home directory or

sudo /home/<your home directory>/NVIDIA-Linux-x86-xxx.xx.run

(The “x” should be your downloaded NVIDIA driver version or press tab to auto detect the name of driver)
Then your can see the installation screen, follow the steps to install the driver.

You should select Accept if you would like to install the Driver.

Here is a optional confirmation, if you do not already installed the driver, this confirmation will not appear.
It is because I upgrade Ubuntu from 9.10 to 10.04 LTS. You need to re-install the driver.
(Fortunately, I upgraded Ubuntu, and I could capture these photos for all of you.)

Installing driver.
Sometimes the installation will prompt some selections, like overwrite some config file, data file, you should select your choice for your settings.

After the installation, NVidia ask us to run nvidia-xconfig to auto update the X. We suggest you select Yes.

Finally, the driver is (re-)installed.

After install the driver
Type

sudo reboot

to reboot your system
and now your screen will select the highest resolution if your installation is success.

(After upgrade the Kernel, you need to re-install the Driver again)

The images below are screen captures when installing NVIDIA Driver.
It is because I recompile the Kernel
and use another computer to remote control my computer to install the NVIDIA Driver.
So I could capture these images.