Thanks to everyone who responded! The current exercise (tearing down desktops, reassembling them, and testing) has been very well received by the students. It keeps them busy and challenged the entire time we have them. Every session has a few students who are convinced that these computers will never work again, and they are all smiles when it is successful. We usually time each team, and the fastest ones get some sort of prize (like an iPod shuffle). We encourage them to try and figure out mistakes on their own (by adding time penalties for help provided by the presenters) A secondary reason for changing this approach is that we have started leasing our equipment instead of buying it outright. So, our supply of computers to use is shrinking quickly. I've gotten a couple very promising suggestions here and I will be sure to report what we ended up doing and the results in this thread in November if anyone is interested.