In all cases i can think of, you always get a COA sticker...
Even my Uni has a sticker on each and every machine...
The disc you talk of is used by orgs such as Unis and system builders, but doesnt really offer much in the way of a discount from M$
So if someone is "giving" these away, i would stay well clear as it doesnt make economic sense...
Would be ok to put OEM on a new HDD as OEM can be distributer via the means of any new hardware and additions subject to some restrictions...
I know of people who have used fake WIN XP Pro/Home since day one, and they have no issues unless they want to download any new updates direct from M$, in whichcase they turn to the many hacked updates out there