Well, if the video in question is being played in RealPlayer, then you can turn off "optimized video display" in Prefrences -> Performance -> Video Card Compatibility and you can then simply use Print Screen or whatever to get the picture.
For Media Player, you have to end up turning off all the video optimizaions for the video. Properties -> Advanced -> Video Renderer -> Properties -> DirectDraw. Turn off all the direct draw options, and you should be able to capture a screen shot.
JigPu