function swapImage( imgId )
{
  document.getElementById( 'bookmark' ).src = imgId;
}
function restoreImage()
{
  document.getElementById( 'bookmark' ).src = 'images/promo/sample_bookmark.gif';
}
function restoreImageInstr()
{
  document.getElementById( 'bookmark' ).src = 'images/promo/sample_bookmark_instr.gif';
}