I would be very careful using the Include tag if the url is set by a GET or POST. Some one could have it grab a page of PHP code to do bad things. But no one would ever do that.
Perhaps something like this would work better.
echo implode("",file($url));
Or you could assign it and then run regex on it, to maybe customize how it appears. (And fix the the <img and <a tags that dont have the url.)
As yet another option, you could do something with Iframes, you can remove the borders and scollbars with options, plus with a little java you could make it fit nice.