function is_numeric(form) {
	var msg = "";
	
	if (form.postcode.value == "") {
		msg += "Please enter a postcode.\n";
	}


	var pc = /^[2-7]\d{3}$/;
	var ntpc = /^0?8{1}\d{2}$/; 
	if (!  (pc.test(form.postcode.value) || ntpc.test(form.postcode.value))) {
		msg += "Please enter a valid postcode in Australia.\n";
	}

	if (msg == "") {
		return true;
	}
	else {
		alert(msg);
		return false;
	}
}