Windows 7: Second monitor not detected through dongle / splitter

Hi all -

First-timer, so hope this is the right forum. I have an Alienware M-17X laptop with an NVidia GeForce GTX 460M graphics card. I'm trying to set up dual monitors through a VGA splitter, and I just can't get the second monitor to be detected. The card is definitely able to detect dual displays, because if I open my laptop and use that as one display, it will recognize that an external monitor is also plugged in and allow me to split the screens that way. If I then plug in the second physical monitor through the dongle, it simply clones the display; so right now what I'm looking at is one independent screen on my laptop itself, and two copies of the second screen on my two monitors.



I have tried:
- updating the NVidia drivers
- running Detect in the Windows display manager
- running Rigorous Detect through the NVidia configuration app
- rebooting
- switching the monitors into different ports on the dongle
- plugging each monitor directly into the VGA port independently
- turning the monitors off and back on
- punching myself in the face repeatedly

None of these options has improved the situation. I would very much appreciate any assistance to avoid the necessity of further self-inflicted damage.

Thanks,
Mike