I recently had a problem with Windows Vista and the nVidia display drivers:
When I logged on to Windows and the dual monitor settings were set correctly (19″ display as primary display and the laptop display as secundary), Vista would reset these settings, setting my laptop display as primary, my stand-alone display as secundary with a resolution based on the laptop display (1280 x 800).
Then I found a fix for this issue, changing a register entry:
The key is in HKLMSoftwareMicrosoftTMM, called
UseIViewHelper and it’s value is 1. Just rename this key and reboot. The problem will be fixed!