How it works is simple, a CSS conditional state checking to see what browser is viewing the page. Just simply add <!--[if IE]> into your CSS, then the IE specific CSS code to fix what IE freaks out on, then close it with <![endif]-->. Pretty simple, no?
<--[if IE]>
position:relative;
<![endif]>
That was placed in the header bar CSS, after the position:fixed; bit.
[edit]Well, seems it isn't working as well as I wanted...[/edit]