$('#background').animate({backgroundPosition: '(10% 250px)'});
Due to some browser bugs (i.e. Firefox, you have to set your (initial) background-position inline:
<div style="background-position: 10px 20px"></div>
Offcurse you can achieve this with JavaScript (jQuery), too:
$('#background').css({backgroundPosition: '10px 20px'});
$('#background')
.css({backgroundPosition: '-60px 0'}) // workaround for FF 2.0 bug
.click(function(){
$(this)
.animate({backgroundPosition: '(500px 150px)'})
.animate({backgroundPosition: '(-20px 250px)'});
});