when i play these files though winamp or media player there is no sound?
Missing codec on windows at a guess.
but copy to xbox and play through xbmc works? why?
Because xbmc rocks (i.e. has the correct codec).
can i do this the other way around ? i would like to use winamp or somthing to watch files from my xbox on my pc.
You can possibly do this via the ftp server.
covers - how do i make them , in xbmp it used to be hold both triggers to capture an image and save as cover?
No, that's not supported in xbmc, though clicking the left thumbstick will take a screenshot.
also when palying video files in xbmp you could speed up and slow down the sound to get it in sync with the video,
i can not find out how to do this in xbmc is it possible?
No. <