The disk is indeed a genuine MS embedded hologram job.
It was somehow stuck in a loop. It wouldn't show the validation code, nor allow the 30 days unactivated access, nor start in safe mode. So, today, I formatted the partition (again) and reloaded it all over again. Surprise, surprise; it let us in to the 30 day period and I followed the go back in and activate option. That gave chance to set up the modem and, as I couldn't stand the possibility of the validation code being invisible for the 3rd reload, the dial direct option was chosen. It worked!
Many thanks to you all for your patient advice and guidance.