var mynav = document.getElementById("nav");
var navitems = mynav.getElementsByTagName("li");
var navcount = navitems.length - 1;
var lastwidth = 54;

function fixupnav() {
    var totalw = 0;
    for (var i=0; i < navcount; i++) {
        if (navitems[i].className.indexOf("active") >= 0) {
            text = navitems[i].childNodes[2];
        } else {
            text = navitems[i].childNodes[0].childNodes[2];
        }
        w = parseInt((mynav.parentNode.clientWidth - lastwidth) / navcount);
        if (w % 2 != 0) w -= 1; // для IE6
        navitems[i].style.width = w + "px";
        totalw += w;
    }
    navitems[navitems.length - 1].style.width = mynav.parentNode.clientWidth - totalw + "px";
}

fixupnav()
window.onresize = fixupnav
window.onload = fixupnav