I have a Sony TFT 17" and a Samsung TFT 15". In the Sony I had the same problem and the resolution ever was forced to 1280x960. With 1280x1024 blank screen, etc...
However, ONE TIME I have found a way to fix the resolution playing with the frequencies. Unfortunately my XConfig is missing and now ever I'm unable to have the Dual view.
BTW, You have some configuration for the two monitors?