asp.net +ajax通信问题。。。。。

代码如下：
<script language="javascript" type="text/javascript">
function js()
{
var UserName = document.form1.TextBox1.value;
var PassWord = document.form1.TextBox2.value;
var url = "/Default.aspx?UserName='" + UserName+"'&PassWord='" +PassWord+"'";
if(document.form1.TextBox1.value=="" || document.form1.TextBox2.value=="")
{
color_err();
}
else
{

createXMLHttpRequest();
XMLHttp.open("GET", url, true);
// XMLHttp.setRequestHeader("content-type","text/xml");
XMLHttp.onreadystatechange = returnResult;
XMLHttp.send(null);
}
}

function color_err()
{
var name_=document.getElementById("floatdiv");
name_.innerHTML="用户名或密码不能为空！";
name_.style.color="red";
name_.style.fontWeight="bold";
}
function login_err()
{
var name_=document.getElementById("floatdiv");
name_.innerHTML="用户名或密码错误！";
name_.style.color="red";
name_.style.fontWeight="bold";
}

var XMLHttp= false;
function createXMLHttpRequest()
{
if(window.ActiveXObject)
{
XMLHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
else if(window.XMLHttpRequest)
{
XMLHttp=new XMLHttpRequest;
}
}



function returnResult()
{
var tt="1";
if(XMLHttp.readyState==4)
{
if(XMLHttp.Status==200)
{
if(tt=XMLHttp.responseText)
{
login_err();
}
}
}
}

</script>

</head>
<body>
<form id="form1" runat="server">
<div id="floatdiv">

</div>


<br />
<br />
　　　　　　　　　　　　用户名　　<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
 　<br />
<br />
　　　　　　　　　　　　　密码　　<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
　<br />
<br />
                                 
　保存　　<asp:DropDownList ID="DropDownList1" runat="server">
</asp:DropDownList>
<br />
<br />
                                   
<input name="button" type="button" value="登陆" onclick="js()" />
　　<asp:Button ID="Button2" runat="server" Text="取消"
onclick="Button2_Click" />
<br />
<br />
<br />


</form>
服务器端代码如下：
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}

protected void Button2_Click(object sender, EventArgs e)
{
this.TextBox1.Text= "";
this.TextBox2.Text= "";

}

protected void rs(object sender, EventArgs e)
{
string UserName = Request["UserName"].ToString();
string PassWord = Request["PassWord"].ToString();
SqlConnection conn = new SqlConnection();
conn.ConnectionString = ConfigurationManager.ConnectionStrings["webtext"].ToString();

SqlCommand cmd = new SqlCommand();
cmd.CommandText = "select * from Hover_Admin where UserName='" + UserName + "' and Password='" + PassWord + "'";
cmd.Connection = conn;

SqlDataReader red = cmd.ExecuteReader();

if (red.Read())
{
Response.Write("1");
}
}



}
现在的问题是怎么向服务端传递参数，服务器又怎么样返回参数给客户端。高手指点一下。好像我写的有点问题？