jquery & php: saving some data without reload

$("#mySpecifikButton").click(function()
{
....some code here...
});

<p><a id="userID">user 0</a></p>
<p><a id="userID">user 1</a></p>
<p><a id="userID">user 2</a></p>
<p><a id="userID">user 3</a></p>
...

<input type="button" value="Button 1" id="1" />
<input type="button" value="Button 2" id="2" />
<input type="button" value="Button 3" id="3" />
<input type="button" value="Button 4" id="4" />

<script type="text/javascript">
$("input[type=button]").click(function() {
  $.post("myPHPscript.php",{buttonID: $(this).attr("id")},function(d) {
    //d is the response from the PHP page.
    //Do something with it!
  });
});
</script>

var xmlHttp;


ajaxFunction(id){

url = anypage.php?Sentid=id; // here you are sending id through GET to any simple db connection mysql and php based page to add to db or anyother function.

xmlHttp.onreadystatechange=stateChanged; xmlHttp.open("GET",url,true) xmlHttp.send(null)

}//end of function


function stateChanged(){
if(xmlHttp.readyState == 4 || xmlHttp.readyState == "complete" ){   	// any operation you want to perform here

    }//end of if
}//end of function


function GetXmlHttpObject(){
var xmlHttp =null;
var xmlHttp =null;
if (window.XMLHttpRequest){

          // If IE7, Mozilla, Safari, etc: Use native object
          var xmlHttp = new XMLHttpRequest()
}
else    {
    if (window.ActiveXObject){

          // ...otherwise, use the ActiveX control for IE5.x and IE6
          var xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
          }

    }
    return xmlHttp;
 }//end of function

<?php
    some_insert_function($_REQUEST["userid"], ...);
?>

function go(el) {
    $.post("/insert.php?items="+el.id);
}