You're going to run into same origin issues trying to style the content of a page loaded from another domain. It may appear to work in some versions of some browsers, but the trend is toward stricter controls on cross domain access.
You can use jquery to pull it into your domain:
<html> <header> <script src="/js/jquery.js" type="text/javascript"> </header> <body> <div id='include-from-outside'></div> <script type='text/ javascript'> $('#include-from-outside').load('http:// example.com/included.html'); </script> </body> </html>
In a noscript stanza you can put the unstyled iframe or iframe a copy pulled to your server periodically.