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 main(action) {
    http.open('get', 'main.php?action='+action);
    http.onreadystatechange = handleResponse;
    http.send(null);
}

function handleResponse() {
    if(http.readyState < 4){
        document.getElementById('loadgif').style.display = "block";
    }
    if(http.readyState == 4){
        document.getElementById('loadgif').style.display = "none";
        var response = http.responseText;
        document.getElementById('main').innerHTML = response;
    }
}