open your video in windows media player 6.4 (start --> run --> mplayer2) and pause
open another instance of wmp 6.4 and open the video again.
go to your scene, alt + prntscrn
paste into favorite image editing program
or
Media Player Classic has an option to "Save image as" which usually does not need the 2 player workaround but if it doesn't work then do the above steps.