window.onload = function() {
    var nav = document.getElementById('nav');
    if(nav) {
        var lnks = nav.getElementsByTagName('A');
        var r = pickRandom(lnks.length);

        nav.className = 'img' + (r+1);

        for(var i = 0; i < lnks.length; i++) {
            lnks[i].desc = document.getElementById('txt' + (i+1));
            lnks[i].index = i + 1;

            if(lnks[i].desc) {
                lnks[i].onmouseover = function() {
                    //nav.className = 'img' + (this.index);
                    this.desc.style.display = 'block';
                }
                lnks[i].onmouseout = function() {
                    //nav.className = 'img' + (this.index);
                    this.desc.style.display = 'none';
                }
            }
        }
    }
}

function pickRandom(range) {
    if (Math.random)
        return Math.round(Math.random() * (range-1));
    else {
        var now = new Date();
        return (now.getTime() / 1000) % range;
    }
}