Quote from Becky Rose :

Hrmm. Clever, but i'm not sure that really counts because underclocking doesnt meen it worked on older hardware. What they've done I would say is created an emulator, which does neatly get around the issue of addressable memory space, but doesn't prove Windows will run on early 80's hardware.

i think youre missing the point a little
the goal wasnt really to prove that they can make xp run on an altair 8800 but to toy around a little and see how slow of a pc they can get away with thats still able to at least boot xp