if (document.images) { 
img1on = new Image();
img1on.src = "header_img_start_green.jpg"; 
img1off = new Image(); 
img1off.src = "header_img_start.jpg"; 
img1green = new Image(); 
img1green.src = "header_img_start_green.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");}
}
function imgGreen(imgName) {
if (document.images) {
document[imgName].src = eval(imgName + "green.src");}
}