Derrick Story writes a superb discussion of how to use a light, low-end digital camera effectively to capture an event like MacWorld Expo.
What the computer press often omits is the point of the exercise: what do we want to accomplish, and how do we think about the task? It's easy to learn to push the buttons; Story tells us what shots we want to get, and how to get them. For example, you need an exterior shot of the venue, right? "The image was captured at 5:34 pm, a great time for "night shots" in the winter. You can add more color to your images if you shoot your night shots before the sky goes completely dark. "