Thank you for your response, but I don't understand. You are suggesting that I *should* use the NVidia closed source driver? That is what I am using. "nvidia" is the closed source one. If I choose the XFree "nv" driver, then TwinView is not available.Driver "nvidia"
VendorName "Nvidia"
BoardName "NVIDIA GeForce 4 MX440"
You do not use the NVidia closed source driver but the nvidia module from XFree. I am sure twinview is only supported / a feature by the NVidia driver. Be sure do deactivate DRI running the nv driver (follow the instructions in the readme on nvidia.com).
This tool produces the same configuration that I already have with respect to TwinView.
Maybe http://yanc.sourceforge.net/ is helpful for you.