Re: 2 video cards with linux/ 2 twinviews
The problem has to do with the XINERAMA protocol extension. You can verify what XINERAMA configuration is being conveyed to your window manager by running:
xdpyinfo -ext XINERAMA
When you use twinview alone, the NVIDIA drivers provide an XINERAMA extension that reports the physical layout of the screens. However, once you enable the xorg xinerama extension, it reports only the virtual geometry of the whole twinview display. In the past, I recall having success using the "TwinViewXineramaInfoOverride" option described in Appendix B.