if (document.images){

var buyOff=new Image();
buyOff.src="images/buyOff.gif";
var buyOn=new Image();
buyOn.src="images/buyOn.gif";

}
function off(linkID) {
        document[linkID].src = eval(linkID + "Off.src");
}
function on(linkID) {
        document[linkID].src = eval(linkID + "On.src");
}