function reShout(){
     $.getJSON(
         "/",
         {page:"getShout",nr:$("#last").val()},
         function(mesgs){
         $.each(mesgs.mesg,function(n,item){
             var newMesg=$("<div>");
             newMesg.addClass("item");
             newMesg.addClass(item.class);
             newMesg.html("<strong>"+item.autor+"</strong> <small>"+item.date+"</small><br/>"+item.text);
             $("#shoutbox").append(newMesg);
         });
         $("#last").val(mesgs.lastNr);
         $("#shoutbox").attr("scrollTop",$("#shoutbox").attr("scrollHeight")-$("#shoutbox").attr("offsetHeight"));
         }
     );
     setTimeout("reShout();",3000);
}
$(document).ready(function(){
$("form[@name='shoutForm']").submit(function(event){
     $.post("/sendMesg",
     {mesg:this.mesg.value},
     function(){
         reShout();
     });
     this.mesg.value="";
     return false;
     event.preventDefault();
});
reShout();
});

<form name="shoutForm" method="post" action="/sendShout">
<div id="box_komunikator">
<div class="box_tytul">&raquo; Komunikator</div>

<div style="height:300px; overflow-y:scroll;" id="shoutbox"></div>

<input type="text" name="mesg" style="width:220px; padding:5px; margin-left:20px; margin-top:20px; border: solid 1px #AB1B15; background:#fff; font: 800 11px tahoma; color:#444; display:block;"/>
<input type="submit" value="Wyślij" style="margin:5px 20px 5px 0; float:right"/>
<input type="hidden" id="last" name="last" defaultValue="0" value="0" />
</div>
</form>