if (document.images)
{
buytickets_on = new Image();
buytickets_on.src = "images/button_buytickets_on.png";
buytickets_off = new Image();
buytickets_off.src = "images/button_buytickets_off.png";

}

 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;
   }
 }