Beautiful! Your solution was 99%... instead of "this.scrollY", I used "$(window).scrollTop()". What's even better is that this solution only requires the jQuery1.2.6 library (no additional libraries needed).
The reason I wanted that version in particular is because that's what ships with MVC currently.
Here's the code:
$(document).ready(function() {
$("#topBar").css("position", "absolute");
});
$(window).scroll(function() {
$("#topBar").css("top", $(window).scrollTop() + "px");
});