For FTP you can use any FTP program. Connect to 'wdtv' or the ip of the wdtv. Use 'root' for the username and no password.
For telnet use either the built in telnet application in windows:
- Start, Run, type 'telnet wdtv', enter
- Login with 'root' and no password
Or you can download putty
which is a very good free telnet program
- Again, connect to wdtv (or the ip of the wdtv) and login with 'root' and no password
You then have root access to your wdtv under Linux. Just search on google for a busybox quickstart, or any linux shell manual. Most command accept '--help' or '-?' for more information. If you are familiar with dos, 'cd dir' is the same and 'ls *.jpg' is similar to 'dir *.jpg'. And you can complete dir/file names with [tab].
There is loads of good information on the web. That is how I got and learned everything. Good luck!