how to define background position for image?

how to define background position for image?

i m using parallex jquery , ....can any one guide how can i define the background position for the foreground image
its cutting in the middle of the page i want it should alwz stick to the bottom of the window size...........Checl My page : http://wonho.agora-me.com/


script :
$(document).ready(function(){
  
  
$('#intro').parallax("50%", 0.3);
$('#second').parallax("50%", 0.9);
          $('.bg').parallax("100%",1.2);

})
</script>
code:
<div id="second" style="z-index:500; "><!-- $(window).scrollTop()-->
<div class="bg"  style="z-index:550; "></div>
<div class="story"  >
</div></div></div>
css:
#second{
background: url(images/About-BG11.jpg) 50% 0 no-repeat fixed;
background-color: white;
height: 1140px;
margin: 0 auto;
overflow: hidden;
padding: 0; z-index:600;
}
#second .bg{
background: url(images/aboutsec1.png)  50% 0 no-repeat fixed;
    /*  height: 1000px;*/
margin: 0 auto;
padding: 0;
position: absolute;
width: 1800px; 

  
margin-top:67px;
/*z-index: 100;*/
}
plz suggest.
thnx