Thanks very much for the ideas.
I tried everything suggested in the stackoverflow.com thread. Unfortunately, none of it worked. Password-protected sharing in Vista was already turned off, and the folder was already shared with Everyone -- these settings made it possible for other Windows computers (ranging from XP to Windows 10) to read the Public folders.
I enabled the Guest account but there doesn't seem to be any way to add it to the list of users who can access the folder. Presumably, though, a "Guest" would be included in "Everyone."
Everything failed with the persistent request (every time I tried to access the Public folder) in the Kubuntu machine to enter a username and password.
The only thing I haven't tried yet is to set up a username and password for the Vista PC (the one with the Public folder I want Linux to access).
I even turned off the firewall and (alternatively) added the Linux box to the firewall's trusted devices. No luck.
