Dunno how good a deal it is, but selling OEM versions of Windows with any major hardware upgrade was part of Microsoft's "Get Legal" program as of last year. Anyway, the proviso of buying some major bit of hardware was and apparently is being ignored by some vendors. Microsoft is clearly very lax on enforcement of this particular deal (why should they care?), and it's not a legal issue for the buyer in any event. How can buying a genuine version from an authorized vendor be illegal for a private citizen? Any onus would be on the vendor, not the buyer.
Pricewatch is full of these deals, some of them cheaper than TC computers. Order just the software, odds are they'll ship it. Oops!