I bet if you take this line out
IE will look more like the other browsers because as it is now its in quirks mode means its likely rendering the css incorrectly. And about your other problems with just a quick glance at the css, you have negative margins on some anchor elements? Why did you do this? You shouldn't have to. Also an undordered list in FF has a left padding, so if you set both padding and margin to 0 for the ul then the uls will look the same in IE and most of the other browsers as well. Just because your code validates doesn't mean its going to display properly. I do believe its the negative margins in your links that are throwing the site off in the other browsers. IE shows you what it thinks you want and the Standards compliant browsers show you what you code.
<?xml version="1.0" encoding="UTF-8"?>