Re: Xinerama, with acceleration
Your usage of the ConnectedMonitor option is incorrect, and that alone might be causing, or at least contributing to the problem you're experiencing. Per the NVIDIA README, the ConnectedMonitor option is meant solely to tell the driver about the existence of a display device that it could not normally probe for/detect on its own when X is started. ConnectedMonitor can *NOT* be used to force a display device to be the primary/secondary/etc display device. Attempts to do so will not work, and potentially confuse the driver resulting in unexpected results.
That said, I'd suggest commenting our your usage of ConnectedMonitor, and seeing if that helps at all.
If it does not, you're going to need to install 1.0-8178. 1.0-7174 is no longer supported for your videocard, and you could possibly be hitting a bug in 1.0-7174 that was long ago fixed in a later driver version.