Here is How i made my USB(4gb)
note: this will boot BT like it's starting from a Disk But only h hell of a lot faster!!
Use RMPrepUSB (v2.1.620) to make it bootable
Use install grub4dos(you may want to download it first)
Use this in menu.lst
Code:
#Main Menu
timeout 30
default 0
title BackTrack 5 KDE 32 \n Start Backtrack 5
kernel /ERDIMG/BT5/casper/vmlinuz file=/cdrom/BT5/preseed/custom.seed live-media-path=ERDIMG/BT5/casper boot=casper textonly noprompt vga=791-- nonpersistent
initrd /ERDIMG/BT5/casper/initrd.gz
title
root ()
title Reboot
reboot
title Shutdown
halt
extract the iso to BT5\ on the root of the flash drive works EVERY-TIME (SEE www.Reboot.pro for more info)
Tested With BT5 KDE 32 && BT5R3 KDE 64