I voted yes but i'm not completely sure on this one....
I bought a copy of Vista Home Premium the day it came out, upgraded from XP MCE 2005 (legit from Gateway) for about a year. I wanted to re-do my computer so I put the disc in, installed it without a key (selected Home Premium, not Ultimate or anything like that), and put my key in when it was done.
Well, my dad has a copy of vista with his computer, which is legal.
All other machines came with XP home edition legal, however i upgraded them to pro from a torrent, so its not totally illegal, just a free upgrade in my opinion.