Hi Kel,
there are numerous approaches to secure FTP, including SFTP, FTPS and various flavors within each of those.
NetTalk, at this point though, doesn't do Secure FTP in either guise, so the short answer is "you can't".
HTTPS is the preferred option for doing secure file transfers (both to and from the server.)
However, you can, if you like, create a secure connection between the FTP client and the server by "tunnelling" over SSH.
Stunnel is a program commonly used for this.
Cheers
Bruce