how to use a directory name to point to a file..

I've seen this done before.. but I'm not sure if the site used pure PHP or not:

It was like this... they had a URL that said something like..

and it would point to..

If you noticed... the directory /membername/ was stored as the variable for $user

How could something like this be done? And can it be done with only PHP?

NOTE: I'm on a windows server running IIS 6

You need to register session membername when the user logs in and then you use
http://members.website.com/profile.php?user=<?=$_SESSION['membername']?>
Hope this help