what do you mean exactly by "scrambled manner"? what is the data type for the column in the datebase, you should be using date.
the code i gave was an example, you need to substitute the correct form elements names. In your form, the data element is named "dateReg", so the code at the top of the page should be:
<?php
if($_SERVER["REQUEST_METHOD"] == "POST") {
$_POST['dateReg'] = "".((isset($_POST["dateReg"]))?date("Y-m-d", strtotime($_POST["dateReg"])):"") ."";
}
?>