Explore Your World: Configure Dual Monitors with nVidia on Ubuntu Jaunty (9.04)

Make sure that the nVidia driver has been installed and is functioning properly on your first screen. Also, make sure both monitors are connected.

Open the command-line terminal Konsole and type:

$ sudo nvidia-settings

Select "X Server Display Configuration".

You should see 3 boxes (2 if your card doesn't have an S-Video out). From here you can configure all of your card's outputs.

Check the "(Disabled)" box.

Select "Configure...".
The most common choice is TwinView. Select it.
Setup the desired screen resolutions and positions of your two active displays.
The new display will likely have resolution set to "Auto" to match your first. Change this if you wish.
Leave the first screen's position as "Absolute" and set your second display's position relative to that.
"Clone" means the same output on both.
Once you are satisfied with your settings, hit Apply to test them.
Note: if your displays are side-by-side, the kicker may extend across both screens as well as any maximized applications. This will be corrected when the X server is restarted.
f everything else is ok, hit "Save to X Configuration File". Now hit Ctrl+Alt+Backspace to restart X. You now have 2 screens!
The NVIDIA X Server Settings application can be also found in K -> System Settings to change settings later, but this does not always work because settings need to be changed as the root user.)
Troubleshooting: if the X server fails to reload you can recover your old X configuration. In a terminal: