function UserNameCheck(site){  
	var xmlHttp;
	var phplink;
	var username = window.document.getElementById('username_M');

	phplink = site + "checkusername.php?u=" + username.value

	try{
		xmlHttp=new XMLHttpRequest();
	}
	catch (e){
		try{
			xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
		}
		catch (e){
			try{
				xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
			}
			catch (e){
				alert("Tarayiciniz AjaX desteklemiyor!");
				return false;
			}
		}
	}

	xmlHttp.onreadystatechange=function(){
		if(xmlHttp.readyState==4)
		{
			setINNER("username_M_span",xmlHttp.responseText);
		}
		else
		{
			setINNER("username_M_span","<span>Kontrol Ediliyor..</span>");
		}
	}

	xmlHttp.open("GET", phplink, true);
	xmlHttp.send(null);
}