DC-In is for power only, maybe an external battery pack.
I wanted to transfer 3 hours worth of old vacation video to DVD recently from a Sony 8mm video camera. After some research I picked up Pinnacle's Movie Studio 8 with their DC10+ video capture card. Capturing went as well as expected, I only lost an average of 1 frame per minute of video (again, from an analog source, I'd say that's pretty good). Editing, rendering, compiling and burning the video to DVD eventually worked out quite well with Studio 8 and now I don't have to worry about loosing any precious memories to deteriorating video tape again.
FWIW, I just bought a new Sony mini DV camera and shot some video over the holidays. Connecting the camera via firewire to my computer, firing up Studio 8 and importing the video was incredibly smooth. I love the fact that you can control the video camera's transport controls right through the software. Also, dropped frames are a thing of the past thanks to firewire. I think I just found myself a new hobby! 😀