JQuery :: Make A "login Bar", Which Will Stay At The Top Of The Page

I'm trying to make a "login bar", which will stay at the top of the page - but when you click it, then it opens up into a nice box. The problem I'm having though, is a weird "blip" when it tries to settle (after clicking it);[URL].. The JS is very simple - so maybe its something with the CSS thats not playing ball?

$(document).ready(function() {
$('#opener_block_link').click( function() {
$('#login_block').slideToggle();
});
});