RE: openssh: Enabling sftp, but disabling ssh?

Does anybody know if it's possible, using openssh, to allow
file transfer to/from a machine, using sftp, for a specific
userid, and disallow ssh login/remote command execution for
that same userid? Other userids on the machine should be unaffected.

You should be able to set the user to an invalid shell (as long as it's
listed in /etc/shells).