After installing video card driver I can't configure multiple monitors...

Hi there,
I've just started using Ubuntu and I have this strange problem.

In windows I use 2 monitors - the main laptop display and Samsung Sync Master. My computer is Asus x73sl.

When I boot Ubuntu, both monitors are working, but in very low resolution and only in mirror mode. After I install the nVidia driver, suggested by Ubuntu, and restart the machine, my laptop screen resolution becomes significantly higher and I can use the full visual effects option. But I'm not able to use the second monitor anymore.

NVIDIA X Server seems to refuse to apply and save any change I try to make in the settings. In X Server Display Configuration I'm able to set the second monitor properly, but when I try to apply the changes, an error message appears. When I try to save the changes to the X Configuration File (and restart the program and/or the computer), no changes take place at all.

Here's what NVIDIA X Server Settings says about the Graphics Card Information:

Graphics Processor: GeForce 9300M GS
VBIOS Version: 62.98.3c.00.54
Memory: 512 MB
Bus Type: PCI Express x16
Bus ID: ?@?:?:?
PCI Device ID: Unknown
PCI Vendor ID: Unknown
IRQ: 16
X Screens: Screen 0
Display Devices: LGD (DFP-0), Samsung SyncMaster (CRT-0)