A couple of things... I noticed the page you provide is just the menu. So, are you including that page on another page?
If not, I know that IE (especially IE6) will have some real problems displaying anything correctly without page declarations such as
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
If you don't make a doctype declaration and define the flavor of html, you will probably have some real issues with IE6.