I can help with that (its also for everyone else looking for it).
This is only for people that have BackTrack 4 installed on a USB drive!
So what happens is that every time we boot a scripts gets called to auto fill in the display drivers (like in the normal live CD) to disable this we need to edit the script and stop it from overwriting our xorg.conf file every time we reboot.
and on the first line insert exit 0 like below
We only add the exit 0 on the top, this will make the script exit as soon as its called. I know there are other options but this allows us if necessary to easily change things back to the good old (without changing a lot of other files)
#dexconf: Debian X server configuration file writer
Hopes that helps ,