$(window).scroll(function() { // 页面发生scroll事件时触发 
var bodyTop = 0; 
if (typeof window.pageYOffset != 'undefined') { 
bodyTop = window.pageYOffset; 
} 
else if (typeof document.compatMode != 'undefined' && document.compatMode != 'BackCompat') 
{ 
bodyTop = document.documentElement.scrollTop; 
} 
else if (typeof document.body != 'undefined') { 
bodyTop = document.body.scrollTop; 
} 
$("#livesupport").css("top", 100 + bodyTop
) // 设置层的CSS样式中的top属性, 注意要是小写，要符合“标准” 
$("#livesupport>span").replaceWith("<a href=\"javascript:void(window.open('http://www.myhome400.com/chat/client.php?locale=en','','width=660,height=550,left=0,top=0,resizable=yes,menubar=no,location=no,status=yes,scrollbars=yes'))\"><img src=\"http://www.myhome400.com/images/livechat/live4.jpg\" width=\"180\" height=\"50\" border=\"0\" alt=\"Click to Get Live Help\" style=\"float:left\"/></a>"
); // 设置层的内容，
});