I have 2 monitors connected to a Win XP SP3 - one through VGA and the other DVI - and they both work - they just have the same image. At first I was using the MB video connectors and thought it couldn't handle 2 so I bought a NVIDIA GeForce 6200 PCI card. No change in results after loading drivers and rebooting. In display properties, settings only sees one - see attached screen shot. So when I go into the settings to try and set them to display both or to identify, the computer only notices one monitor.
I did uninstall, reinstall, update, etc drivers multiple times with multiple restarts. There were several codes in Device manager - after all the updates the error in the current device status of device manager says "This device cannot start. (Code 10)"
Of course now my mouse is unresponsive and jumpy... hopefully the monitor solution will also remedy that.