After a lot of digging with the same problem, I have realized that nVidia intentionally has removed this feature from their 8xxx and forward cards, and also for any users of previous generations of cards if you're using a driver newer then the 174.xx ones.
If I had known of this I certainly wouldn't have thrown 350$ at my current output-crippled BFG 8800GTS 512MB card, and I'm too late for getting any refunds for it in exchange of an ATI card. This is certainly a dealbreaker for me, if I had read about this crippled TV-output in reviews I'd probably not have gotten this card.
If any AT staff or reviewers read this post: I'd certainly be very interested in knowing the reasons why nVidia removed this feature. Is it anything that you could inquire about? I'm sure they'd listen to you more then a disgruntled consumer with no market power or connections to any bigger news/hardware site.
Any other AT readers: Do you know of any other application or 'hack' that can show any played videos on your primary monitor to do a full screen video overlay on your secondary monitor / TV? EDIT: For clarification, I'm looking for some freeware software / hack that could help with this for nVidia cards, I'm very happy with using media player classic as it is... I don't want yet another bloated media player.
See
this help topic in nVidias knowledgebase.