How long have you let the machine sit? I know that if Join Domain is failing due to bad credentials or some other problem, Windows will try over and over for 15 minutes before bailing out and moving on.
Boot the machine back into WinPE (no job assigned) or mount the drive on a different machine. You'll want to look at C:\Windows\Panther and read all the log files, including the ones in subfolders of Panther (Unattend, UnattendGC, setup.exe, etc). Also look at the logs in C:\Windows\Debug\
If it hangs during Windows Setup, you most likely have an issue with your Unattend.xml