if (document.images) {

// static
    img1off = new Image();
    img1off.src = "img/nav_com.gif";
    img2off = new Image();
    img2off.src = "img/nav_res.gif";
    img3off = new Image();
    img3off.src = "img/nav_con.gif";
    img4off = new Image();
    img4off.src = "img/nav_pro.gif";
    img5off = new Image();
    img5off.src = "img/nav_cu.gif";

// mouseover
    img1on = new Image();
    img1on.src = "img/nav_com_over.gif";
    img2on = new Image();
    img2on.src = "img/nav_res_over.gif";
    img3on = new Image();
    img3on.src = "img/nav_con_over.gif";
    img4on = new Image();
    img4on.src = "img/nav_pro_over.gif";
    img5on = new Image();
    img5on.src = "img/nav_cu_over.gif";

}

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

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