How do you make a div follow as you scroll?

You can either use the css property Fixed, or if you need something more fine-tuned then you need to use javascript and track the scrollTop property which defines where the user agent’s scrollbar location is (0 being at the top … and x being at the bottom)

.Fixed
{
    position: fixed;
    top: 20px;
}

or with jQuery:

$('#ParentContainer').scroll(function() { 
    $('#FixedDiv').css('top', $(this).scrollTop());
});