A user posted about this.  I was going to reply in the post but decided to make another post.  Maybe someone knows what is going on with these two media players.

I'm seeing the same thing happen.  Any captures showing the video area of Windows Media Player or Winamp come out black where the video should be. I never realized until now, but even a Print Screen and pasting to a paint app doesn't capture the video portion of WMP or Winamp.  I had added the record function to stress test it one day and just left it in after capturing from Quicktime.  I never even thought to try it on other media players. 

There is something even more odd. If you open a captured image of one of these two media players in (so far) any paint program and move it over WMP or Winamp while a movie is playing, you can see through the paint program.  The area of the captured image where the video frame should of been shows the current video through it.  It's like it is transparent, but only for the video.  It also happens with Divx and the older Windows Media Player 5.1.

This has peaked my curiosity.  I'll be looking into it.  Does anyone know what Winamp and WMP does different than Quicktime?  Is it possibly some sort of rights management or layered windows thats causing this behaviour?

[update]
Looks like it's hardware acceleration / hardware video overlay that causes it. In Windows Media Player, under the performance tab, slide the video acceleration to something less than full. In Winamp, under Video Options, uncheck 'Allow hardware video overlay'. This should allow you to take screenshots with any program.