Chris Harper said:
> Try checking the video overlay settings for the adapter. Any  
> settings you can modify in regards to this will most likely lead to  
> the solution.

This was the closest to the mark.  Turns out that the "cloning"  
feature of this dual-DVI card does not exactly clone video to both  
ports.  Only the primary port will play some videos (other videos do  
play on both primary & secondary ports, we still do not know why).   
When we changed the setting to make screen 2 (analog) the primary and  
screen 1 (digital) the secondary, videos then showed on screen 2 but  
not screen 1.  This is not ideal, but turns out to be good enough to  
run our brain imaging tasks as we need screen 1 only for a control  
screen.

OTOH, some may argue that the dual-port card does clone videos to both  
ports, but just not to both analog & digital outputs, that would also  
fit our results.  We probably will not test this though.

Thanks to all for helping out.

-- dkm