Sharepoint 2007 - set a datefield based on the content of another datefield?

Sharepoint 2007 - set a datefield based on the content of another datefield?

Hi all - I am new here, and I use Jquery for MOSS 2007 work.  I have been able to make some simple stuff work (hiding fields, hiding table elements, etc), but I have an issue that i would LOVE to be able to make work, and despite hours of searching, I can't figure it out.  What I have is a form that is similar to a calendar, with descriptions, sales rep, etc, and two date fields.  'Rental Dates - Start' and 'Rental Dates - End'.  What happens is that 'Rental Dates - Start' can be many months in the future, and the end date would always be AFTER the start date... when someone selects the start date, how can I make the "end" date default to that (to minimize the clicking necessary to set the end date).
 
What I tried is this (obviously after the jquery call):
 
<script>
    $(document).ready(function(){
       $(":input[title='Rental Dates - Start']").focusout(function ()

            {
             var NewDate = $(this).val();
             )}.focustout();
       $(":input[title='Rental Dates - End']").val(NewDate);
    });
</script>





It obviously doesn't work (since I am posting here), but I can't figure out why not or how to make it work...
 
Any suggestions?  Thanks!