If you mean client side then you will have to use JavaScript or frames.
Simple way to start, try jQuery
$("#links").load("/Main_Page #jq-p-Getting-Started li");
More at jQuery Docs
If you want to use IFrames then start with Wikipedia on IFrames
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>Example</title>
</head>
<body>
The material below comes from the website http://example.com/
<iframe src="http://example.com/" height="200">
Alternative text for browsers that do not understand IFrames.
</iframe>
</body>
</html>