z1on = new Image;
        z1on.src = "image/button-home-over.jpg";

        z2on = new Image;
        z2on.src = "image/button-products-over.jpg";

        z3on = new Image;
        z3on.src = "image/button-contact-us-over.jpg";
        
        z1off = new Image;
        z1off.src = "image/button-home.jpg";    

        z2off = new Image;
        z2off.src = "image/button-products.jpg";    

        z3off = new Image;
        z3off.src = "image/button-contact-us.jpg";   
                                     
function img_act(imgName) 
{
        imgOn = eval(imgName + "on.src");
        document [imgName].src = imgOn;
}

function img_inact(imgName) 
{
        imgOff = eval(imgName + "off.src");
        document [imgName].src = imgOff;
}