What do you mean with "unzipped to USB"? How did you do that? I assume that your problem lies here, you don't have to unzip anything, you are supposed to copy the file to USB using unetbootin. How you can put the live-iso to USB you can read here
and you install it from this live-USB medium to harddisk you can read here
All that information is available on Backtrack's webpage, that should always be the first point where to look at, if having problems with Backtrack.