If they open in Winamp or Windows Media Player, another solution is to open a dummy video first, keep this one paused (i.e. not stoppped and keep the window on the screen, not reduced), then you will be able to use Printscreen key to grab picture from the second video (the good one), that you open in a second window of Winamp / Windows Media Player. I do not think that Winamp lets you open two times itself, so you may have use Windows Media Player for the first dummy video.