//Nas propriedades da página em Advanced:
<script language="javascript" type="text/javascript" src="http://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.7.2.min.js"></script>
<script language="javascript" type="text/javascript">
$(document).ready(FUNCTION(e) {
$('Input').keydown( FUNCTION(e) {
var key = e.charCode ? e.charCode : e.keyCode ? e.keyCode : 0;
IF(key == 13) {
e.preventDefault();
var inputs = $(this).closest('form').find(':Input:Visible');
inputs.eq( inputs.index(this)+ 1 ).focus();
}