Trying to Inline Validate with onblur but message wont appear

Question

I am trying to do an inline validation, it worked with alert but we need error message to appear on top of submit button not an alert box.

JS Function

function validateEmail(username) {
    var reg = /^([A-Za-z0-9_-.])+@([A-Za-z0-9_-.])+.([A-Za-z]{2,4})$/;
    if (reg.test(username.value) !== false) {
        $("#msgbox").fadeTo(200,0.1,function() {
            //add message and change the class of the box and start fading

            $(this).html('Invalid username / password...').addClass('messageboxerror').fadeTo(900,1);
        });
    }
    return false;
}