function getBrowserWidth() {
    if (window.innerWidth) {
        return window.innerWidth;
    }
    else if (document.documentElement && document.documentElement.clientWidth != 0) {
        return document.documentElement.clientWidth;
    }
    else if (document.body) { return document.body.clientWidth; }
    return 0;
}


function dynamicLayout() {
    var browserWidth = getBrowserWidth();
    if (browserWidth < 800) {
        document.getElementById('header').style.width = '745px';
        document.getElementById('subnav1').style.width = '745px';
    }
}

function AddHandler(element, eventName, browserHandler) {
    if (window.addEventListener)
        element.addEventListener(eventName, browserHandler, false);
    else if (element.attachEvent)
        element.attachEvent('on' + eventName, browserHandler);
}

AddHandler(window, 'load', dynamicLayout);