jquery 怎样实现div 的滚动条自动滚动?

问题
在div中有一张很长的图片，宽度有 12000 ，我想让这div 的滚动条自动滚动.这javaScript不知该怎写，
还请各位路过的高手指点...^_^

<!DOCTYPE HTML>
<html>
<head>
<meta charset="gb2312" />
<title></title>
<style>
div {
width:100px; height:100px;
overflow:scroll;
}
</style>
</head>
<body>
<div id="t">
<img src="http://avatar.profile.csdn.net/1/D/5/2_fnsx_wfs.jpg" width="1200" />
</div>
<script>
var $ = function(id){
return document.getElementById(id);
};
var obj = $('t');
var i = 1;
setInterval(function(){
obj.scrollLeft = i
obj.scrollTop = i
i += 5;
}, 30)
</script>
</body>
</html>
这个意思？
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.7.2.min.js"></script>
<script type="text/javascript">
var scrollLeft = 0;
function autoScroll(i) {
var o = $("#demo");
if (o.scrollLeft() == $("#demo img").eq(0).width - 200) clearInterval(t);
else {
scrollLeft += i;
o.scrollLeft(scrollLeft);
}
}
$(document).ready( function() {
var t = window.setInterval('autoScroll(1)', 10);
});
</script>
</head><body>
<style type="text/css">
#demo {
width:200px;
overflow:scroll;
}
</style>
<div id="demo"><img src="http://pic16.nipic.com/20110909/2238196_094518206167_2.jpg" /></div>
<span id="scrollLert"></span>
</body>
</html>
//var t = window.setInterval('autoScroll(1)', 10);
t = window.setInterval('autoScroll(1)', 10);