Ajax?

...

<script type="text/javascript">

var url = "getCityState.php?param="; // The server-side script to be called

// What to do with the returned data, this I understand
function handleHttpResponse() { 
    if(http.readyState == 4) { // If the http object has done its thing
        // Split the comma-delimited response into an array
        results = http.responseText.split(",");
        var cityText = document.createTextNode(results[0]);
        var stateText = document.createTextNode(results[1]);
        var cityRef = document.getElementById("city"); // The first span
        cityRef.replaceChild(cityText,cityRef.lastChild);
        var stateRef = document.getElementById('state'); // The second span
        stateRef.replaceChild(stateText,stateRef.lastChild);       
    }
}

// Call the server-side script - need to study the open and send functions
function updateCityState() { 
    var zipValue = document.getElementById('zip').value; // From the form
    http.open("GET", url + escape(zipValue), true);
    http.onreadystatechange = handleHttpResponse;
    http.send(null);
}

// Cross-browser goodness, not sure I want to understand it...
function getHTTPObject() { 
    var xmlhttp;
    /*@cc_on
    @if (@_jscript_version >= 5)
        try {
            xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
        } catch (e) {
            try {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (E) {
                xmlhttp = false;
            }
        }
    @else
    xmlhttp = false;
    @end @*/
    if (!xmlhttp && typeof XMLHttpRequest != 'undefined') {
    // this part is clear enough
        try {
            xmlhttp = new XMLHttpRequest();
        } catch (e) {
            xmlhttp = false;
        }
    }
    return xmlhttp;
}

// We create the HTTP Object that gets used in the function updateCityState()
var http = getHTTPObject(); 
</script>

...

<form action="post">
    <p>
    ZIP code:
    <input type="text" size="5" name="zip" id="zip" onblur="updateCityState();" />
    </p>
</form>
    City: <span name="city" id="city"> </span><br />
    State: <span name="state" id="state"> </span>
...

var data, io;

io = new IOElement();

data = {
	myvalue : "My Name, is 'Mary'"
}

io.post("mypage.php",data,fnCallBack);

function fnCallBack(e,success) {
	if (success) {
		var o = e.getSource();
		var rt = o.getVariable('serverSays');
		alert(rt)
	}
	// retry ?
}