I downloaded the 6.6 GB file from the Shack, extracted it using Windows 7's plain ol' native extractor, and tossed it over the network to my brother's Windows XP machine, no problems at all.
I am a free account user, I don't use a DL manager, I don't use UAC, and I was in Firefox if those tidbits can help anyone.
Glad to be here, and I hope you all can be with us soon!!
(I downloaded it at about midnight-1am CST, could they have had a corrupted file up earlier in the day? I DO recall a few relaunched demos over the years over there to clear up corruptions, maybe they'll clean this one up!)