Just relating a problem and the fix I used.
I did a clean install of Win 7 64bit on my computer that had Vista 32bit. Install went great. I went to NVidia and downloaded the Win 7 64bit driver and software.
At first it seemed to be working great, then I connected the external monitor. Would not let me select the external monitor only. Only option that would work was both monitors at the same resolution at the same time.
Uninstalled NVidia driver and software, and installed Dell's NVidia software for Vista 64bit.
Works like it should now.
Just wanted to share.