if (document.images) {
 navBGon = new Image(); navBGon.src = "img/nav-bg-on.gif";
 navBGoff = new Image(); navBGoff.src = "img/nav-bg.gif";
 casinoNight = new Image(); casinoNight.src = "img/casino_night.jpg";
}

function rollOver(object) {
 document.getElementById(object).style.backgroundImage = "url("+navBGon.src+")";
}

function rollOut(object) {
 document.getElementById(object).style.backgroundImage = "url("+navBGoff.src+")";
}

function openAd() {
 document.getElementById('ad').style.visibility='visible';
 document.getElementById('adbg').style.visibility='visible';
}

function closeAd() {
 document.getElementById('ad').style.visibility='hidden';
 document.getElementById('adbg').style.visibility='hidden';
}