Code:
var xmlHttp

/* Process Username */
function processUsername(str)
{
        if (str.length==0)
        {
                document.getElementById("usernameStatus").innerHTML="";
                return;
        }
        xmlHttp=GetXmlHttpObject();
        if (xmlHttp==null)
        {
                alert ("Browser does not support HTTP Request");
                return;
        }
        var url="ajax_server/processUsername.php";
        url=url+"?q="+str;
        url=url+"&sid="+Math.random();
        xmlHttp.onreadystatechange=usernameStateChanged;
        xmlHttp.open("GET",url,true);
        xmlHttp.send(null);
}
function usernameStateChanged()
{
        if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
        { document.getElementById("usernameStatus").innerHTML=xmlHttp.responseText; }
}

/* Process Password */
function processPassword(str)
{
        if (str.length==0)
        {
                document.getElementById("passwordStatus").innerHTML="";
                return;
        }
        xmlHttp=GetXmlHttpObject();
        if (xmlHttp==null)
        {
                alert ("Browser does not support HTTP Request");
                return;
        }
        var url="ajax_server/processPassword.php";
        url=url+"?q="+str;
        url=url+"&sid="+Math.random();
        xmlHttp.onreadystatechange=passwordStateChanged;
        xmlHttp.open("GET",url,true);
        xmlHttp.send(null);
}
function passwordStateChanged()
{
        if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
        { document.getElementById("passwordStatus").innerHTML=xmlHttp.responseText; }
}

/* Process Gender */
function processGender(str)
{
        if (str.length==0)
        {
                document.getElementById("genderStatus").innerHTML="";
                return;
        }
        xmlHttp=GetXmlHttpObject();
        if (xmlHttp==null)
        {
                alert ("Browser does not support HTTP Request");
                return;
        }
        var url="ajax_server/processGender.php";
        url=url+"?q="+str;
        url=url+"&sid="+Math.random();
        xmlHttp.onreadystatechange=genderStateChanged;
        xmlHttp.open("GET",url,true);
        xmlHttp.send(null);
}
function genderStateChanged()
{
        if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
        { document.getElementById("genderStatus").innerHTML=xmlHttp.responseText; }
}

/* Process Email */
function processEmail(str)
{
        if (str.length==0)
        {
                document.getElementById("emailStatus").innerHTML="";
                return;
        }
        xmlHttp=GetXmlHttpObject();
        if (xmlHttp==null)
        {
                alert ("Browser does not support HTTP Request");
                return;
        }
        var url="ajax_server/processEmail.php";
        url=url+"?q="+str;
        url=url+"&sid="+Math.random();
        xmlHttp.onreadystatechange=emailStateChanged;
        xmlHttp.open("GET",url,true);
        xmlHttp.send(null);
}
function emailStateChanged()
{
        if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
        { document.getElementById("emailStatus").innerHTML=xmlHttp.responseText; }
}

/* Refresh Server Status */
function refreshServerStatus(str)
{
        if (str.length==0)
        {
                document.getElementById("serverStatus").innerHTML="";
                return;
        }
        xmlHttp=GetXmlHttpObject();
        if (xmlHttp==null)
        {
                alert ("Browser does not support HTTP Request");
                return;
        }
        var url="ajax_server/refreshServerStatus.php";
        url=url+"?q="+str;
        url=url+"&sid="+Math.random();
        xmlHttp.onreadystatechange=serverStatusStateChanged;
        xmlHttp.open("GET",url,true);
        xmlHttp.send(null);
}
function serverStatusStateChanged()
{
        if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete")
        { document.getElementById("serverStatus").innerHTML=xmlHttp.responseText; }
}

/* General Ajax Function */
function GetXmlHttpObject()
{
        var objXMLHttp=null;
        if (window.XMLHttpRequest)
        {
                objXMLHttp=new XMLHttpRequest();
        }
        else if (window.ActiveXObject)
        {
                objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP");
        }
        return objXMLHttp;
}
How can i optimize this javascript Ajax code so that im not repeating blocks of code again and again where small variable name changes...?