from Nvidia's own faq:
"HDCP Capable:
Designed to meet the output protection management (HDCP) and security specifications of the Blu-ray Disc and HD DVD formats, allowing the playback of encrypted movie content on PCs when connected to HDCP-compliant displays:
To enjoy the ultimate HD DVD or Blu-ray experience on a PC, you’ll need:
* PCI Express graphics card with secure HDCP CryptoROM and GeForce 7 Series HDCP-capable GPU with 256MB of graphics memory or GeForce 8 Series HDCP-capable GPU with 128MB of graphics memory
* NVIDIA ForceWare graphics drivers that feature PureVideo HD technology
* An optical disc drive that supports Blu-ray and/or HD DVD movie playback
* Blu-ray or HD DVD movie player software with PureVideo HD hardware acceleration of H.264, VC-1, and MPEG-2 high-definition content
* A dual-core CPU is recommended with the GeForce 7 Series
* 1GB of system memory is recommended under Windows XP; 2GB is recommended under Windows Vista. "
The fact that Nvidia now make specific mention that their new cards have this support, suggests two things, 1) yes you will need it, and 2) if they dont list it for your product, chances are it doesnt have it.
Thats not to say that you cant sometimes run SD DVD across HDMI with non-HDCP equipment, but if any of the components require HDCP (and most of the new stuff now does), then every piece in the chain needs to support it.
Cheers