how about adding a little on TCP/IP
maybe do a little packet sniffing and let them see the TCP/IP process and how connection is created and closed. Knowing what is in a packet can give them a little more of an understanding on how hacking utilities work.
I would start out at the bottom of the OSI layer and work your way up.
example, start with ICMP and work your way up through IP, TCP, UDP and DNS.
Have them use a Kinnopix disk and run ethereal. Ethereal is pretty sweet, does all the decoding for you.