function CheckForm(f) {
    if (!f['cb'].checked) {
        alert("Please click on checkbox first!");
        return false;
    }
	if (f['firstname'].value == "") {
		alert("Please enter a value for field First Name");
		f['firstname'].focus();
		return false;
	}
	if (f.email.value == "") {
		alert("Please enter your email address.");
		f.email.focus();
		return false;
	}
	if (!/^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$/.test(f.email.value)) {
		alert("Email is invalid");
		f.email.focus();
		return false;
	}
	return true;
};