Plug the drive into a running computer and copy over the files on the XP disk to the drive. Then install free dos or something on the drive or use a DOS floppy or flash drive. When you boot, type the following into the DOS prompt:
Nothing is really hidden but the files are archived or compressed and some files or maybe invisible but no big secrets. WINNT.exe is the way you install windows XP from DOS. Windows XP before or after you install it has a lot of programs you can't see Tons of tricks you can do.