Cannot capture video, but will control camera...

Ok here's the deal. A friend of mine is having trouble with his DV camcorder and firewire capturing. He is running a 2800+ with XP SP2. Here's what we've tried so far:

1) 2 different brands of camcorders and all different settings (not a camcorder compatibility problem)
2) 2 different firewire cards, with and without generic drivers (not a firewire card problem)
3) 3 different video capturing programs, Pinnacle 9, Ulead, and Windows Movie Maker...all with the latest patches (not a software issue)
4) 2 different firewire cables (not a bad cable)
5) Re-installing this that and the other...the software, video drivers, directx, you name it.

The camcorder is recognized by XP and setups fine. All the software recognizes the camera and will even operate it (fast forward/rewind). However when the camera is played or capturing is begun, nothing shows up on the preview screen and nothing is captured. It's as if it's not recieving the actual data. To make me even more upset, the same setup (card, cable, camera, software) all work fine on my machine which has similar specs and XP with SP2. So it's apparently not necessarily a Service Pack 2 issue.

Anyway, if any can shed some light on what is causing this problem I'd me much obliged. Thanks!