Url I See Doesn't Map To File Layout On Server.

I've been asked to update a site whose web author is no longer available. I have the ftp details, but when I ftp in I can not see a structure that matches the URL I see when visiting the site through a browser.

A sample URL is http://www.****.org/~issw2004/issw_general/2006.php

But the file structure I see when I go into the server using ftp, has issw2004 way down the directory, with no ~ preceding it (what does the ~ mean?), and it is empty of files or children folders.

I've tried doing a global search of the site for both the file name, and some text that that file contains, but both return empty.

So, I'm stuck. I know little about URL rewriting, and apart from knowing that files can be hidden or paths rewritten, don't know where to start in 'finding' the file I need to change!