Bonjour, voici ce que la doc du WAIK dit :
By default, the built-in administrator account is disabled in all default, clean installations.
For Windows® 7 and Windows Vista®, you can enable the built-in administrator account during unattended installations by setting Username to Administrator
(only the English word, Administrator, automatically enables the account). This enables the built-in administrator account, even if a password is not specified in AdministratorPassword. If a password is specified in AdministratorPassword, then
use the same password in Autologon.
Donc il faut bien mettre administrator dans la version française.