if (document.images) {

img1on = new Image();
img1on.src = "img/d_logo_a.jpg";
img1off = new Image();
img1off.src = "img/d_logo.jpg";

img2on = new Image();
img2on.src = "img/e_logo_a.jpg";
img2off = new Image();
img2off.src = "img/e_logo.jpg";

img3on = new Image();
img3on.src = "img/i_logo_a.jpg";
img3off = new Image();
img3off.src = "img/i_logo.jpg";

img4on = new Image();
img4on.src = "img/t_logo_a.jpg";
img4off = new Image();
img4off.src = "img/t_logo.jpg";

}
function imgOn(imgName) {
if (document.images) {
document[imgName].src = eval(imgName + "on.src");}
}
function imgOff(imgName) {
if (document.images) {
document[imgName].src = eval(imgName + "off.src");}
}