I've seen that before. But in a slightly different way.
The URL can be something like this:
http://forum.fok.nl/showtopic.php/52481/3/25
So you can pretend de variable to be a directory!! I'm looking for how this is done, but still haven't found the awnser.
I'm writing a mail at this time to contect the owner of the website.
I'll keep in thouch with you....