For this, you'll want to combine two concepts:
The first is having a div that shows at the top of the page. Take a look at this tutorial, which shows you how to place <div>s over top of each other. Essentially, you'll want your info bar placed at the top with a z-order of something larget than everything else in the same spot.
Once you have it where you want it, you'll then need to fade it in or out. This article will show you what is required to fade in/out divs using javascript.
Just set the area's opacity to 100% and fade it in when the page loads. Then have a link or button that calls the javascript to fade out if you want to close it (or do it after a certain time).