Barry,
I think FrontPage has an option that will read the entire site down to local files on your disk. That will get you going with what's there now, then you modify it, and Publish it provided the ISP will accept the way FP wants to send the files, or you have to use ftp in a DOS window to logon and send the files. There are also some Windows ftp programs, but the one that ships with Win95/98 works well enough for small sites.
>What do I have to know (other than the URL),to get to the client's webpage so that I can make modifications? Obviously, if I call up their existing site, I can view the source code but can't modify it. Is it just a question of having access to their server, or is it more complicated than that? (They also used MS FrontPage).