if (document.images) {

//on
img1on = new Image();
img1on.src = "images/mainr_06.gif";

img2on = new Image();
img2on.src = "images/mainr_07.gif";

img3on = new Image();
img3on.src = "images/mainr_08.gif";

img4on = new Image();
img4on.src = "images/mainr_09.gif";

img5on = new Image();
img5on.src = "images/mainr_10.gif";

img6on = new Image();
img6on.src = "images/mainr_11.gif";

img6bon = new Image();
img6bon.src = "images/mainr_12.gif";

//off
img1off = new Image();
img1off.src = "images/main_06.gif";

img2off = new Image();
img2off.src = "images/main_07.gif";

img3off = new Image();
img3off.src = "images/main_08.gif";

img4off = new Image();
img4off.src = "images/main_09.gif";

img5off = new Image();
img5off.src = "images/main_10.gif";

img6off = new Image();
img6off.src = "images/main_11.gif";

img6boff = new Image();
img6boff.src = "images/main_12.gif";

}
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");
}
}