[System.Web.Services.WebMethod]
public static string VeryUserName(string name)
{
string rtn = "恭喜，此帐号还没有注册，你可以使用。";

if (name == "")
rtn = "请填写一个注册帐号。";

if (name == "Insus.NET")
rtn = "此用户已经注册，请使用另外帐号。"; 

return rtn;
}

<asp:TextBox ID="TextBoxAccount" runat="server"></asp:TextBox><br />
<input id="btnrReg" type="button" value="注册" onclick="VeryRegAccount()" />

<script src="scripts/jquery-1.3.2.min.js" type="text/javascript"></script> 
<script type="text/javascript"> 
function VeryRegAccount() { 
$.ajax({ 
type: "POST", 
url: "Default.aspx/VeryUserName", 
data: '{name: "' + $("#<%= TextBoxAccount.ClientID%>")[0].value + '" }', 
contentType: "application/json; charset=utf-8", 
dataType: "json", 
success: OnSuccess, 
failure: function (response) { 
alert(response.d); 
} 
}); 
} 
function OnSuccess(response) { 
alert(response.d); 
} 
</script>