Site dropdown menu does not work in IE8 compatibility mode

Hello there, I am working on a site that has a menu that looks great in new browsers, and even IE8 on vista, however in IE8 compatibility mode or in XP for example, the navigation does not work.

I’ve made a jsfiddle here to see what I mean (sorry, am in a hurry; hover over the "result" part and you’ll see the dropdown in action)

http://jsfiddle.net/K3PFd/

It just doesn’t work in compatibility mode or I’m assuming older versions of IE. Of course the client is using IE8 which is why I have to fix this…

Can you PLEASE help?