function validate()
        {
            var error = 0;

            var message = document.getElementsByTagName("span");
            var ck_username = /^[A-Za-z0-9_]{5,15}$/;
            var ck_password = /^[A-Za-z0-9_]{6,20}$/;
            var username = document.myform.username;
            var password = document.myform.password;

            if(!ck_username.test(username.value)) {
                message[0].setAttribute("style","visibility:visible");
                error = 1;
            }
            else {
                message[0].setAttribute("style","visibility:hidden");
                error = 0;
            }
            if(!ck_password.test(password.value)){
                message[0].setAttribute("style","visibility:visible");
                error = 1;
            }
            else {
                message[0].setAttribute("style","visibility:hidden");
                error = 0;
            }

            if (error == 0) {
                return true;
            } else {
                return false;
            }
        }
    </script>