Nope. You can scale non D-Theater via firewire. You'd have to do D-Theater as an analogue input, which no one currently makes, afaik. I've been keeping my eye on this but nothing has popped up yet.
You can scale non copy-protected DVHS tapes (tapes you make, or HD-net tapes) via HTPC. As Wes said, D-Theater tapes and other copy protected tapes cannot be scaled by HTPC as the vcr will not send the data over firewire to the PC in those cases.
HD Leeza or Faroudja will work, as they do have HD analog inputs.
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