if (document.images) {
  btn_audio = new Image();
  btn_audio.src = "inc/btn_audio.gif";
  btn_audio_on = new Image(); 
  btn_audio_on.src = "inc/btn_audio-over.gif";

  btn_video = new Image();
  btn_video.src = "inc/btn_video.gif";
  btn_video_on = new Image(); 
  btn_video_on.src = "inc/btn_video-over.gif";
}


function rollOver(imgname) {
  if (document.images)
    document.images[imgname].src = eval(imgname + '_on.src');
}
// mouse out
function rollOut(imgname) {	
  if (document.images)
    document.images[imgname].src = eval(imgname + '.src');
}