function validate(f)
{
    if (f.username.value == "")
    {
        alert("Please enter your user name");
        f.username.focus();
        return false;
    }

    if (f.password.value == "")
    {
        alert("Please enter your password");
        f.username.focus();
        return false;
    }

    // All fields are OK

    return true;
}