function createRequestObject() {
    var ro;
    var browser = navigator.appName;
    if(browser == "Microsoft Internet Explorer"){
        ro = new ActiveXObject("Microsoft.XMLHTTP");
    }else{
        ro = new XMLHttpRequest();
    }
    return ro;
}

var http = createRequestObject();

function update_registration_email() {
    var email = document.getElementById('address').value;
    http.open('get', 'registration_options.php?email='+email);
    http.onreadystatechange = update_registration_options;
    http.send(null);
    document.getElementById('upgrade_progress').style.display = 'block';
    document.getElementById('upgrade_button').style.display = 'none';
}

function update_registration_options() {
    if (http.readyState == 4) {
	var response = http.responseText;
	document.getElementById('upgrade_options').innerHTML = response;
	document.getElementById('upgrade_progress').style.display = 'none';
	document.getElementById('upgrade_button').style.display = 'block';
    }
}