定位于网页右边的图片（不随滚动条移动）

$(function () {
  var user = $.trim($("#header_logout span").eq(0).html());
  var url = "http://xxx.com/web.php?arg=book&style=1&username=" + user;
  $("<div id='kf' style='position:absolute;right:3px;top:300px;z-index:99999;'><a target='_blank' href='" + url + "'><img width='73px' height='147px' src='/images/kf.gif' border='0' /></a></div>").appendTo("body");
  setPosition();
  $(window).scroll(
    setPosition
  );
});

function setPosition() {
  var h = (window.innerHeight) ? window.innerHeight : (document.documentElement && document.documentElement.clientHeight) ? document.documentElement.clientHeight : document.body.offsetHeight;
  var top = (h - $("#kf").height()) / 2;
  $("#kf").css("top", top + $(window).scrollTop());
}