browser_name = navigator.appName;
browser_version = parseFloat(navigator.appVersion);

if (browser_name == "Netscape" && browser_version >= 3.0) {
 	roll = 'true';
  	}
  
else if (browser_name == "Microsoft Internet Explorer" && browser_version >= 4.0) {
    roll = 'true';
	}

else { roll = 'false';} 

function  on(img,ref) {if (roll == 'true') {document.images[img].src = ref;}} 
function off(img,ref) {if (roll == 'true') {document.images[img].src = ref;}}