@Bob I've actually been skimming through the pages first, and came across this:
From Windows PE, a previous version of Windows, or another preinstallation environment, run Setup.exe with the explicit path to the answer file. If you do not include the path to the answer file, Setup.exe searches for a valid answer file in several specific locations. For more information, see Windows Setup Command-Line Options.
Well, I guess it contains a setup.exe then somewhere?