IE 7 navigation issues – positioning changes

I am having trouble with my horizontal nav menu in IE7. You can visit my website here: restorethemajority.com . The li divs have an image as a background, and there is a red gradient background behind those images that is a part of the main background image. It looks fine on the main page, but when you navigate to a different page, the positioning of the nav menu, as well as the content div below it, shift downward 10 pixels or so. Can anyone explain why this happens? Is there a quick fix for it? Thank you for your help in advance.

Ben