How to fit image size with user browser height

[h_classen (Hans-Gerd Claßen)]

have a look over here:

Creating a Fixed Header Image

I am trying to create a fixed image for the header of a website, but I am not finding a CSS hack that has worked within Hype yet. To see what I mean, view the image at the top of this page and scroll down: http://guitarjo.com/ Any ideas on how to target images within Hype to create this effect?