Without commenting on the legitimacy of Ebay tapes, I'm pretty sure that HBO had a catalog listing for copies of the special when it was 1st broadcast (winter of 96-97).
There very well could be legitimate copies but from reading the eBay ads, it sure doesn't seem as if these are. Some of the descriptions make a point of explaining away the lack of packaging for the tapes as if to try to take away from any suspicion the buyer might have that it is an illegal dub. Though promo tapes might not have any bells and whistles in the packaging, I would think that copies that HBO sold in their catalog would have a proper case/box. Again, the sudden appearance of these tapes on eBay makes me suspicious. However, if there are legitimate copies available, I wonder if they contain the entire show as there were a few pieces cut from the show that actually aired. Does anyone know?
I remember a story of someone informing Jay of a seller who had digitized "Cards as Weapons" and was selling CDs. Jay's attitude(as I recall it; all of this is second hand) was since the book isn't in print, it didn't really bother him that someone was making it available this way. Maybe he doesn't care about the HBO special (although maybe HBO does . . . ).
I keep a pretty good eye on eBay and the one time that I saw a digitized "Cards as Weapons" on eBay, it ended up being pulled from the auction block. There has been a rumor that "Cards as Weapons" is going to be reprinted so having an illegal digitized version floating around probably wouldn't be appreciated.