Is the backtrack 4 pre final kenrel compiled with PAE support set ? If not you will need to recompile the kernel with Physical Address Extension Physical Address Extension - Wikipedia, the free encyclopedia.
If it is, post output of
And ..Code:dmesg | grep e820
and ..Code:free -l
and last but not leastCode:dmidecode -t 16 dmidecode -t 17
Code:lspci -v


