if (document.images) {

	bt1on = new Image();           // Active images
	bt1on.src = "images/bt1.gif";
	bt1off = new Image();          // Inactive images
	bt1off.src = "images/bt1-ro.gif";

	bt2on = new Image();           // Active images
	bt2on.src = "images/bt2.gif";
	bt2off = new Image();          // Inactive images
	bt2off.src = "images/bt2-ro.gif";

	bt3on = new Image();           // Active images
	bt3on.src = "images/bt3.gif";
	bt3off = new Image();          // Inactive images
	bt3off.src = "images/bt3-ro.gif";


  }
    function imgOn(imgName) {
            if (document.images) {
                document[imgName].src = eval(imgName + "off.src");
            }
    }
    function imgOff(imgName) {
            if (document.images) {
                document[imgName].src = eval(imgName + "on.src");        
            }
    }