The identifiers (all throughout the config file) have exactly zero influence on anything. They're only there to identify certain section instances to other sections.
For example, your ServerLayout section is referencing Screen "Screen". This is the only thing that cares about what the Identifier in the screen sections is -- it'll bind this ServerLayout to the Screen section that has an Identifier "Screen" in it.
Changing the Identifier in your Device section will (at best) do nothing different, and (at worst) make the X startup fail because the Screen section can no longer find its Device.
Does it help to get rid of the v4l module, in your Modules section?
Does it help to get rid of all the unused stuff in your Device section as well, like VendorName, BoardName, and BusID? None of these should be required, except for BusID, and that one only is if you have more than one video card. And make SURE you change "nv" to "nvidia" -- it's still "nv" here.
Post a log file, too, from right after changing all this stuff (and the driver back to "nvidia"). Make the changes, shut down X (do this from runlevel 3, BTW -- if a display manager is running, that might screw stuff up), then startx, then (after the lockup) reboot to runlevel 3 again, and cp /var/log/XFree86.0.log .
Then change the config file back (or do whatever you have been doing to read these boards) and attach the log file that you copied to your home directory.