<script type="text/javascript">
function test(){
        try {
            oPageRequest=new XMLHttpRequest();
            } catch (e)  {
                try {
                    oPageRequest=new ActiveXObject("Msxml2.XMLHTTP");
                    } catch (e) {
                        try {
                            oPageRequest=new ActiveXObject("Microsoft.XMLHTTP");
                            } catch (e) {
                                alert("Je browser ondersteund deze actie niet.");
                                 return false;
                            }
                    }
            }
            oPageRequest.open("GET","test.php",true);
            oPageRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

            oPageRequest.onreadystatechange=function() {
                if(oPageRequest.readyState == 4 )
                    {
                        document.getElementById('testz').innerHTML = oPageRequest.responseText;
                    }
                }
            oPageRequest.send(null);

}
</script>
<div id="testz">Test</div>
<input type="button" onclick="test();" value="NAO" />