Just get the untouched torrents and you're fine. I compared hashes and they come up clean, so they would have been borderline no-lifes to fiddle with the OS while keeping the MD5 and SHA-1 the same.
The guys running a torrent server with a bootleg version of windows 7 are far a too well-rounded group of gentlemen to throw a rootkit in there and generate a new MD5 hash.
But seriously, I'm running Windows 7 64 and I really can't tell the difference between it and Vista 64. My Vista is a fresh install as well. I had a dual boot XP/Vista set up which I wiped since I moved to Vista full time at this point.
I only have a dual core chip here. Maybe it's more obvious with quads.