Disbale Form Submission on JQuery

Disbale Form Submission on JQuery

Hi,
 
I am using following code to validate forms fields as well as name availability using jQuery and Ajax.
However, I need to disable form submission if the product name isn't available.
 
Please help ASAP
 
The code is as follows:
 
$(document).ready(function(){
$("#frmFamily").validate();
$("#fmlyName").change(function() {
var usr = $("#fmlyName").val();
if(usr.length >= 4)
{
$("#status").html('<img src="../../images/loader.gif" align="absmiddle">&nbsp;Checking availability...');

    $.ajax({
    type: "POST",
    url: "checkavailability.php",
    data: "fmlyName="+ usr,
    success: function(msg){ 



   $("#status").ajaxComplete(function(event, request, settings){
 if(msg == 'OK')
 { 
       // $("#fmlyName").removeClass('object_error'); // if necessary
  //$("#fmlyName").addClass("object_ok");
  $(this).html('&nbsp;<img src="../../images/tick.gif" align="absmiddle">');



 }
 else
 {
  //$("#fmlyName").removeClass('object_ok'); // if necessary
  
  $("#fmlyName").addClass("object_error");
  $(this).html(msg);
 } 






   });
 }
  });
}
else
 {
 $("#status").html('<font color="red">' +
'The Family name should have at least <strong>4</strong> characters.</font>');
 $("#fmlyName").removeClass('object_ok'); // if necessary
 $("#fmlyName").addClass("object_error");
 }






});
});