• správně by se měl uvádět typ skriptu, ale v HTML5 se jako default bere text/javascript

<script type="text/javascript">
..
</script>

• http://jecas.cz/ajax
• XMLHttpRequest

var http_req = new XMLHttpRequest();
var url = "myscript.php";
var params = "myparam=myparamvalue";
var displaybox = document.getElementById("display").innerHTML;
 
displaybox ="<h3>Loading data ...</h3>";
 
http_req.onreadystatechange=function() {
  if (http_req.readyState==4 && http_req.status==200) {
    displaybox = http_req.responseText;
  }
}
 
http_req.open("POST",url,true);
http_req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
http_req.send(params);