(function($){
    $.fn.center=function(settings){
        var style=$.extend({
                          position:'absolute',//absolute or fixed
                          top:'50%',            //50%即居中，将应用负边距计算，溢出不予考虑了。
                          left:'50%',
                          zIndex:2009,
                          relative:true        //相对于包含它的容器居中还是整个页面
                          }, settings || {});
        return this.each(function(){
                  var $this=$(this);                  
                  if(style.top == '50%') style.marginTop=-$this.outerHeight()/2;
                  if(style.left == '50%') style.marginLeft=-$this.outerWidth()/2;
                  if(style.relative && !$this.parent().is('body') && $this.parent().css('position') == 'static')
                      $this.parent().css('position','relative');
                  delete style.relative;
                  //ie6
                  if(style.position == 'fixed' && $.browser.version=='6.0')
                  {
                      style.marginTop += $(window).scrollTop();
                      style.position = 'absolute';
                      $(window).scroll(function(){
                                                    $this.stop().animate({
                                                                      marginTop:$(window).scrollTop()-$this.outerHeight()/2
                                                                      });
                                                    });
                  }
                  $this.css(style);
                  });
    };
})(jQuery);