I haven't completely figured out how to get access to the video stream in WinNT.
I'm using Video for Windows with a Connectix QuickCam, as well as an Intel Video Capture Card, and it seems to assume that you are only writing to a file or previewing into a window.
Windows tries to take over the system and doesn't really provide any stable hooks (unlike IRIX). If anyone knows how to deal with this, please let me know.