(function($){  
$.fn.xFixed = function(params){  
var defaults={  
top:200,  
left:150,  
noCss:false,  
interval:200, 
animateDuration:220  
};  
defaults = $.extend(defaults,params);  
var done = false;  
//如果是IE6  
if(($.browser.msie&&$.browser.version=='6.0'))  
{  
done = true;  
}      
return this.each(function(i,o){  
var $this = $(this);  
this.fixPosition = function(){  

var st = $(document).scrollTop();  
//var sl = $(document).scrollLeft();  
$this.animate({top:st+defaults.top},{queue:false,duration:defaults.animateDuration});                
};//fixPos    
if(done)  
{  
$this.css({position:'absolute',top:defaults.top});  
setInterval(this.fixPosition,defaults.interval);  

}  
else  
{  
$this.css({position:'fixed',top:"50%"});  
}      
});//each 
};//xFixed  
})(jQuery);