Disappearing div

I've been working on a template for a site here at work. It's a two column layout with a header and footer. I borrowed liberally from A List Apart to create the CSS. For the most part it's working and looks great in Firefox. However, in IE the content of my menu/rail isn't showing. I'm guessing it's hidden behind the content window. Can anyone help me figure out how to make it stop doing that?

The site
The CSS

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