$("#tbEmail").change(function() {
var usr = $("#tbEmail");
var pattern = "^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$";
if(eregi(pattern, usr)){
$("#status").html('<img src="loader.gif" align="absmiddle"> Checking availability...');
....