yes,
you can configure port 80 to be ftp on the server, but you will not be able to get around the ftp://x.y.z:80 limitation.
Reason is, port 80 is defined as a http port by most commercial browser clients, and may have difficulty recognizing ftp. May work though, worth a shot.
If that doesn't work you could just let them use 80 over http and in IIS allow directory browsing. If you disable script and execute privlages for all files, remove all appication mappings, hack your matabase to disable the ASP engine to not start on that website, remove all ISAPI functionality, and use other security mechanisms, unless they are hitting an html page it should function exactly like an ftp server with both netscape and IE.
Not saying I would do that, but hey you asked for an option.
Good Luck,
Galrahn
galrahn@galrahn.com