if (document.images)
{
btn1_on = new Image();
btn1_on.src = "images/btn1on.jpg";
btn1_off = new Image();
btn1_off.src = "images/btn1off.jpg";

btn2_on = new Image();
btn2_on.src = "images/btn2on.jpg";
btn2_off = new Image();
btn2_off.src = "images/btn2off.jpg";

btn3_on = new Image();
btn3_on.src = "images/btn3on.jpg";
btn3_off = new Image();
btn3_off.src = "images/btn3off.jpg";

btn4_on = new Image();
btn4_on.src = "images/btn4on.jpg";
btn4_off = new Image();
btn4_off.src = "images/btn4off.jpg";


}

 function rollOn(imgName)
 {
   if (document.images) {
    imgOn = eval(imgName + "_on.src");
    document [imgName].src = imgOn;
   }
 }

 function rollOff(imgName)
 {
   if (document.images) {
    imgOff = eval(imgName + "_off.src");
    document [imgName].src = imgOff;
   }
 }