Thanks for this. It was a bit more complicated than I anticipated and I had to muddle through the manual, but knowing it was possible was helpful and appreciated.
In my opinion, this is a very valuable, poorly documented, feature of the device considering that many people are paying quite a bit for online sharing of documents.
For those with an interest, the default folder is named, "share". It has all my critical documents on it, so it is password protected and I do not wish to share the password, but I sometimes need to share files with others that are too big to email.
I logged into to the GUI, as suggested, created a new folder that I called, "share2", then adjusted the permissions to make this folder available to anyone. For my host computer to be able to view this folder, I had to map it, which is explained in the manual. From what I can tell, the only way to add a file to this folder (share2) from a remote computer via www.buffalonas.com is to be logged in, so others can only download the file, not upload files to the folder. Thus, it does not appear this folder can be abused by others.
Sorry not to provide more specific step by step instructions, but a very useful feature for those needing to share large files.