You should apply position: fixed
to this box.
Fixed Positioning
An element with fixed position is positioned relative to the browser window.
It will not move even if the window is scrolled.
Here's a sample: http://www.w3schools.com/css/tryit.asp?filename=trycss_position_fixed
You can read more about CSS positioning here: http://www.w3schools.com/css/css_positioning.asp
Here's a jsFiddle that I baked for your that shows how you can get this working: http://jsfiddle.net/leniel/8ub7s/2/
You can see that even when you scroll, the title is still visible and if you hover it, the ad box will show. Just adapt the CSS to your needs as you want it floated to the left. :)