$('#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: '20% 0'}
).click(function(){
$(this).animate({backgroundPosition: '(right 150px)'}, function(){
$(this).animate({backgroundPosition: '(10% 250px)'});
});
});