So it is immediately obvious that you should use SSH rather than telnet, you will find that all the University Servers accept SSH. Redhat 7 ships with an SSH server by default, for other versions you will need to obtain one.
http://www.openssh.com/
If you want a list of free SSH software try http://www.freessh.org/ - especially if you want to find out about Windows SSH clients.
SSH has as special feature that allows it to tunnel other connections over it's (encrypted) ssh connection. So, say, for example you wanted to download your email via IMAP from sable you could tunnel your enencrypted POP3 traffic over and encrypted SSH connection with the following command:
ssh -L 1143:sable.ox.ac.uk:143 kebl1088@sable.ox.ac.uk
You could then tell your email software to download the email from 'localhost' port '1143' and SSH would automatically accept the connection, and then encrypt it before making the connection to the IMAP server on sable. If you are on the wrong end of a modem connection you might want to add in `-C' which will compress the connection as well as encrypt it.