IF AN EXPERT SAYS IT CAN'T BE DONE GET ANOTHER EXPERT.
Backtrack 5 is out so you can check it, comment and share your thoughts about it here.
So lets go right to the business.
Today I`v tried to use Backtrack 5. I made a live usb boot and tried to boot from it. After choosing "Default" option from the GRUB menu, I always saw black\blank screen and computer seems to be stuck. I started to dig and Google for some results and suddenly I found some posts about the subject... couple of suggestions seems to be the answer, but I realized that aren't. One of the answers did help me:
Re: Screen getsblack after startx and Caps lock LED start flashing
I got a Acer Aspire 4820TG and I had the same problem. I removed the vga=7xx entry and wrote vesa instead, and startx worked properly.
So actually you just need to change:
menu label OLDDefault kernel /ubnkern append initrd=/ubninit file=/cdrom/preseed/custom.seed boot=casper text splash vga=791--
menu label Default kernel /ubnkern append initrd=/ubninit file=/cdrom/preseed/custom.seed boot=casper text splash vesa--