[phpmattk]

Don't know how this would involve asynchronous java and xml. Joking aside, you'll have to create a page somewhere called emailtofriend.php, and include the required files (look at one of the other .php pages to see how its done), then at the bottom of the page, do a

$smarty->display("blah/send_to_friend.tpl");

You'll probably have to find some way to pass the url of the page you want to email to the popup page with the form on it. I believe when the send to friend is included, it will send the url of the page its on (ie sendtofriend.php), rather than the page on which your popup link was clicked.