Here are some resources if you want to teach students about the parts of a computer.
http://www.scratch.mit.edu/projects/watiwara/27182 – an interactive application written in Scratch that students can use to learn what the parts of a computer are and how they fit into the overall scheme of things.
http://www.quia.com/hm/86691.html – computer parts hangman game
http://www.kids-online.net/learn/click/table.html – click on parts of the computer to bring up info about that part
http://www.practicalpc.co.uk/computing/what/parts.htm – what are the parts of a computer written for beginners
http://www.tpub.com/content/elecequipment/TM-5-6350-280-23P/img/TM-5-6350-280-23P_21_1.jpg – high level block diagram of a computer