Finally found a solution to the problem with loading the nVidia drivers on a BT4 R1 Live Usb install. The driver would install successfully but not *load* on reboot.
It was not the 'casper-rw' loop file but 'xorg.conf' being wiped out on boot. Just the way the Live USB/CD install works.
I found a reference somewhere to modify '.profile' to copy the correct 'xorg.conf'. Here's my '.profile' :-
This allows X to load the correct driver on my laptop and still be dynamic on any other system.
# remove xorg.conf backup files
# get video card from pci scan
PciScan=$(lspci | grep 'VGA');
# check for NVIDIA video card and copy xorg.conf
if [[ $PciScan == *'Quadro FX 3800M'* ]]; then
cp -f /etc/X11/xorg.conf.Quadro.FX.3800M /etc/X11/xorg.conf;