You can create a jquery function that loads the result in the div you want.
it would be something like the following:
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js"></script> //Include the jQuery Library
<script type="text/javascript">
function load_cart(x) // Create your function with a value to recognize who's cart is it... lets say the customer id value as a parameter
{
$('#cart').load('cart_cont.php',{ //#cart is the id of the div (or any element) you want to load the result
s_id : x //s_id:x - s_id is the value you will get with $_POST['s_id']; in your php file
}); //x is the parameter you send to the function when calling it i.e. load_cart(2)
} //cart_cont.php should have your php code that returns the result
</script>