I did this very thing a few years ago (2006) when I gave video-chatting a go. Instead of using my limited-resolution webcam, I connected an actual video-camera to the input of my TV tuner (an ATI AIW).
There should be a VFW option to select the video source independent of the application, especially if you are using the correct WDM drivers for the tuner. If not, then you could try using alternate drivers like BTWinCap to hopefully provide a different interface.
Another options is to use a virtual/emulated camera. The ones that I tried were VirtualCamera, TrackerCam, and specifically (and free) SplitCam. They create a virtual device that emulates a webcam. That way you can use it as the source in a program, and have the stream provided by whatever source you select with its own, interface outside of the destination program (some allow you to use pictures or videos in addition to a video feed).
(I learned of these because some of the people in the video-chat rooms were using pre-recorded videos instead of a live webcam.)