I am using JQuery ui with datepicker and when a user tabs on to a field, they appropriately get the calendar pop up.
Thanks for the suggestion Jeff, I modified your onSelect function to use the attribute filter to retrieve only elements with the tabindex specified by "nexttab".
$(function(){
  $(".date").datepicker({
      onSelect: function(){
          currenttab = $(el).attr("tabindex");
          nexttab = currenttab * 1 + 1;
          $("[tabindex='" + nexttab + "']").focus();
      }
  });
});
PS: If you don't have tabindexes specified in your code, like I neglected to do earlier, simply add the following code:
$('input, select').each(function(i, val){
    $(this).attr('tabindex', i + 1);
});