$('#idIndicator').fadeIn(300);
$('#idIndicator').fadeOut(300);

$('#idIndicator').css({opacity:0,display:'block'}).animate({opacity:1},300);
$('#idIndicator').animate({opacity:0},300, function() {$('#idIndicator').css({display:'none'});});

	function SendPOST()
                {
		            var data = document.getElementById('text').value;
                    ajaxSendPOST('/system/adminpanel/preview.php','q='+encodeURI(data), SendCallback);
                }
				
				
     function SendCallback(xmlh,query) 
	            {
				    if(xmlh.status == 200)
					  {
                 	     var ans = query;
                         alert(ans);
                         var sel = document.getElementById('result_preview');
					        sel.innerHTML = "";						 
	                  }else{alert("Ошибка");}
                     
					  
					  					  
                }
				
     function ajaxSendPOST(xmlpage,data,callback)
                {
				
                    var xmlh = null;
                    if(window.XMLHttpRequest)
                    xmlh = new XMLHttpRequest();
                    else
                    try
                    { xmlh = new ActiveXObject('Msxml2.XMLHTTP'); }
                    catch(ex) { xmlh = new ActiveXObject('Microsoft.XMLHTTP'); }
					
                    if(xmlh)
                        {
                            xmlh.open('post', xmlpage, true);
                            xmlh.onreadystatechange = function(x) 
							
							{ 
							
							if(xmlh.readyState==4) 
							{
							callback(xmlh,xmlh.responseText); 
							}
							
							
							}
                            
							
							xmlh.setRequestHeader("Accept-Charset", "windows-1251");
                            xmlh.setRequestHeader("Accept-Language","ru, en");
                            xmlh.setRequestHeader("Connection", "close");
                            xmlh.setRequestHeader("Content-length", data.length);
                            xmlh.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
                            xmlh.send(data);
							var sel = document.getElementById('result_preview');
					        sel.innerHTML = "<img style='display: none' src='/system/skins/images/ajax.gif' />";
							$("#ajax").click(function () {
                            $("#result_preview").show("slow");
                             });
							 
	
                        }					
}

   <label>
		   <script src="/system/skins/js/preview.ajax.js" type="text/javascript"></script>
		   <script src="http://code.jquery.com/jquery-latest.js"></script>
		   <div onClick="SendPOST();" id="ajax">Нажми меня</div>
		   <div id="result_preview"></div>
		   
           </label>

$('#loadIndicator').animate({opacity:1}, 500);

$.ajax({
		
		url: url,
		cache: false,
		async: true,
		dataType: 'html',
		type: 'post',
		data: data,
		
		complete:function(data){
				
				$('#loadIndicator').animate({opacity:0}, 500);
				
				d = data.responseText;
				
				alert(d);
			
		}
		
});	

complete:function(data){
				
//вызово модального окна
			
		}