Fun and Informative Way to Introduce Open Source?

jwg asks: "I work in an office environment where I provide technical services and solutions to my co-workers (as I am sure most Slashdot readers do at their respective places of employment). Once a month, we have a round-table meeting to discuss pressing issues in our office. At the beginning of these meetings, it is one person's job to provide some form of 'professional development', usually an activity or game to teach some skill, idea, or trend directly related to their job. My turn is coming up soon, and I would like to introduce my co-workers to the idea (and to some, the way of life) of Open Source. There are many examples of Open Source software and communities out there to reference (Mozilla, Wikipedia, MySQL and... oh yeah, Linux), but has anyone come up with or come across a method to introduce it in a quick, fun, and informative way to a wide variety of people each of which possess a even wider range of technical skill? Did I mention it has to be fun?"