if (document.images) {       
            img11up = new Image();      
            img11up.src = "../img/bu_ess.gif"; 
            img12up = new Image();      
            img12up.src = "../img/bu_home.gif"; 
            img13up = new Image();      
            img13up.src = "../img/bu_back.gif"; 

            img11dn = new Image();      
            img11dn.src = "../img/bu_ess2.gif"; 
            img12dn = new Image();      
            img12dn.src = "../img/bu_home2.gif"; 
            img13dn = new Image();      
            img13dn.src = "../img/bu_back2.gif"; 
        }



// Function to 'activate' images.
function imgOn(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "dn.src");
        }
}

// Function to 'deactivate' images.
function imgOff(imgName) {
        if (document.images) {
            document[imgName].src = eval(imgName + "up.src");
        }
}

function essMouseOver(){
        imgOn('img11');
}

function essMouseOut(){
        imgOff('img11');
}

function homeMouseOver(){
        imgOn('img12');
}

function homeMouseOut(){
        imgOff('img12');
}

function backMouseOver(){
        imgOn('img13');
}

function backMouseOut(){
        imgOff('img13');
}