function comment_here(post_id) {
  var post = document.getElementById("post" + post_id);
  var divs = post.getElementsByTagName('div');
  for(var i=0; i<divs.length; i++) {
    if(divs[i].className == 'new_comment') {  
      divs[i].innerHTML =
        '<form method="post" action="/comment">' +
        '<input type="hidden" name="post_id" value="' + post_id + '"/>' +
        '<input name="body" size="60"/>' +
        '<input type="submit" value="Save Comment"/>' +
        '</form>';
    }
  }
  post.getElementsByTagName('input')[1].focus();
}