var scrWidth = 640;
var scrHeight = 440;
var winWidth = 400;
var winHeight = 200;

if (document.all || document.layers) {
    scrWidth = screen.availWidth;
    scrHeight = screen.availHeight;
}

var leftPos = (scrWidth - winWidth) / 2;
var topPos = (scrHeight - winHeight) / 2;
var optionString = 'resizable=no,directories=no,status=no,location=no,toolbar=no,menubar=no,scrollbars=no,width=' + winWidth + ',height=' + winHeight + ',top=' + topPos + ',left=' + leftPos;

function launch_subscribe() {
    window.open('subscribe.html', 'subscribe_window', optionString);
}