Um, what? You can
dl the firmware separately, sure somebody has the link. You can't just put the hd firmware on the old Zunes due to hardware differences and you can't just copy and paste parts of the HD firmware into the old firmware because that changes the hash of the file and without updating the signature (which you need either a ton of computing power + time or Bill Gate's approval) you have the hardware check which will kill anything youdo.
The reason there's such a negative attitude about Zune hacking isn't because MS doesn't approve it, it's because we've tried and every time we hit MS' security. I heard rumors of an exploit from a well known member here, however either he magically "forgot about it" after being sooo uptight about other people not getting the credit or he was lying about it.
So to sum it up, Non-MS firmware needs either a hardware hack, or a very clever exploit (the common of which have been tried)