Have you followed the official Wiki guides on how to get Backtrack running of an USB flash ?
So, I have a laptop, brand new, running a dualboot with ubuntu and windows 7. Ive downloaded Backtrack 5 both GNOME and KDE in ISO format. I have a USB flash drive, and when I put either one on it and choose to boot from my USB, all my computer says is that is cant find system operative. any help?