I'm guessing that it is a problem with your IEE1394 drivers. I have two IEE1394 ports on my vista machine. One on a video card, and one on the motherboard. My motherboard IEE1394 easily recognizes my camera. The video card one does not. WHen I looked, there were two different drivers. Some cameras are picky about which Firewire drivers they talk with..
If you search google, with specifics, including your make and model of camera, and look up and see what your firewire driver is, you may find your answer..
There are lots of variables..