var ElementWithManualHover = Behavior.create({
    onmouseenter: function() {
        this.element.addClassName('iehover');
    },
    onmouseleave: function() {
        this.element.removeClassName('iehover');
    }
});
var ie6 = (/MSIE\s6/).test(navigator.appVersion);
if (ie6) {
	Event.addBehavior({
       '#menu li': ElementWithManualHover 
    });
}