as sure as I can be with a sample size of 1!
I ran my computer for a while with nv drivers - no hang.
I ran it a while longer on nvidia drivers only displaying to crt - no hang
I then ran it a (short) while with only dvi lcd connected - no hang.
Since then I've only run on nvidia drivers with both dvi and vga connected (dual screen - NOT twinview). It has hung about 8 times all in exactly the same way (as described in 1st post) and more than normal graphics activity ( once an "ls -alR /" was enough to trigger it!) gives me a pixellated/blocky screen with no way to recover from the keyboard. I have to log in remotely and halt the box to recover (the Gainward Ti4200 must be hard reset). This last time, after reboot, the lcd panel was gone.
It doesn't take much imagination to see that that wild pixellation on the screen could be overdriving the lcd panel.
Unless I hear from other Dell UltraSharp 2000fp owners that this beautiful display is defective...