function checkSubmit() {
    var frm = document.forms[0];
    var lastname = frm.lastname.value;
    var firstname = frm.firstname.value;
    var organisation = frm.org.value;
    var email = frm.email.value;

    if (firstname == '') {
        alert('Please enter a name.');
        return false;
    }
    if (lastname == '') {
        alert('Please enter a name.');
        return false;
    }
    if (organisation == '') {
        alert('Please provide us with the name of your organisation.');
        return false;
    }
    if (email == '') {
        alert('Please penter a valid e-mail address.');
        return false;
    }
}