Does it have to be FTP? Can't you just create an HTML page with links to your files? That would be read-only access for the public to download your files. With FTP access, the public would also be able to upload or overwrite your files, which is not desirable.

By default, things on a web site are accessible to the public. I suppose that the top level (root) directory could be open, running a landing page with "public" and "private" directory links. The "private" directory would be password protected, while the "public" would not. Would that work for you?

In your index.html file:

<a href="dir_with_files/file_name_1.ext">This file is blah blah blah</a>

for each file. Assuming you don't have a tremendous number of files, and don't change them too often, it wouldn't be hard to write and maintain such a page. That's just a start... you can add some descriptive text, you can a "thumbnail" image instead of the text link, and you can do all sorts of other things. If you have no idea how to write a page, buy an "HTML page editor" such as Dreamweaver or Expression Web, or download a free one like Nvu.