Working with a background image for player

I came across this great youtube tutorial yesterday for adding a background image to the player.

http://www.youtube.com/watch?v=7yNVXdRQCVU

 I love the idea of the storyline presentation playing so that it looks like its on the monitor and you're able to utilize more space.  The problem is how to get it to work regardless of the the browser window size.  If the browser is resized then the storyline canvas doesn't line up with the monitor or whatever else you have on your background image that you want it to line up with.  Anyone have any ideas how to get the canvas and background image to scale together so the canvas is always on the same location relative to the background image?  

Thanks