var xmlHttp

function confirm_join(str)
  {
var r=confirm('Are you sure you want to do this?/nYou have '+str+' changes left.')
  if (r==true)
    {
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null)
  {
  alert ("Your browser does not support AJAX!");
  return;
  }  
  
aid=document.getElementById("aid").value;

var url="alliance_join.php";
url=url+"?confirm=1&aid="+aid;
xmlHttp.onreadystatechange=stateChanged;
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
    } else { alert('okay'); }


}


function stateChanged() 
{
if (xmlHttp.readyState==3)
{ 
document.getElementById("join").value='Joining...';
}
if (xmlHttp.readyState==4)
{ 
  document.getElementById("join").value='Try again';
     if (xmlHttp.responseText == 'Success') {
     window.location = join_alliance.php?success=1;
     document.getElementById("join").value='Joined';
     document.getElementById("join").disabled='disabled';
     document.getElementById("error").innerHTML='Done';
     }
     else {
     document.getElementById("error").innerHTML='An unknown error occured';
     }
}
}

function GetXmlHttpObject()
{
var xmlHttp=null;
try
  {
  // Firefox, Opera 8.0+, Safari
  xmlHttp=new XMLHttpRequest();
  }
catch (e)
  {
  // Internet Explorer
  try
    {
    xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
    }
  catch (e)
    {
    xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
return xmlHttp;
}



---------------

		<input type="hidden" value="<?=$_GET[aid]?>" id="aid"/>
		<input type="button" value="Join" onClick="confirm_join('4')" id="join"/>