function CheckUserName()
{
var url = '/checkusername.aspx';
var username = $("Username").value;
var pars = 'username=' + username;
var myAjax = new Ajax.Request( url, { method: 'get', parameters: pars,onComplete:showResponseUser});
} 
function showResponseUser(cstr) 
{ //put returned XML in the textarea
	//var node = cstr.responseXML.getElementsByTagName("City");
	
	try{
		alert(cstr.responseText);
		/*$(a.toString()).add(new Option("所有","-1"));
		for(var i=0;i<node.length;i++){
				$(a.toString()).add(new Option(formatTextText(node.item(i)),formatTextValue(node.item(i))));
									}
		for(i=0;i<b.length-1;i++){
			if(a.toString() == b[i]){
										AjaxCity(formatTextValue(node.item(0)),b[i+1]);
										break;
									}
								}*/

		}
	catch(e){
		alert("请输入用户名！");
	}
 }