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

if (browser_name == "Netscape" && browser_version >= 3.0) {
    rollover = 'true'; 
    }
else if (browser_name == "Microsoft Internet Explorer" && browser_version >= 4.0) { 
    rollover = 'true';
    }
else { 
    rollover = 'false';
    }
if (rollover == 'true') {
    grafik1=new Image();grafik1.src="roll1.gif";
    grafik2=new Image();grafik2.src="roll2.gif";
    }

function ro_in(img,ref) { 
    if (rollover == 'true') { 
        document.images[img].src = ref; 
    }
}

function ro_out(img,ref) {
    if (rollover == 'true') {
        document.images[img].src = ref;
    }
}