jaaniic'ša pierakstu klade

CSS
html, body{
height:100%;
min-height:100%;
margin:0;
padding:0;
}
.bg{
width:100%;
height:100%;
background: #fff url(..) no-repeat fixed 0 0;
overflow:auto;
}
<div class="bg">
< span >..< /span >
</div>
Javascript
$('.bg').scroll(function() {
var x = $(this).scrollTop();
$(this).css('background-position', '0% ' + parseInt(-x / 10) + 'px');
});

Check working example at http://jsfiddle.net/Vbtts/
Click this link for the full screen example: http://jsfiddle.net/Vbtts/embedded/result/