I'll start afresh if Saab doesn't mind, cos this is esentially a different issue to the one I started about Prem v Pro.
Funnily enough, I got this link from the MS W7 Forum, which I joined when I got the RC to play with. I didn't look here first because...well, because of who they are. I never imagined such open discussion would take place on a MS forum.
In short, it was legal/acceptable to use OEM on home-builds, but now everything is being done to hush this oft used concession.
Go down to the highlighted bit, but then also read just below.
Is it OK to use OEM Windows on your own PC? Don't ask Microsoft | Ed Bott’s Microsoft Report | ZDNet.com