So what you are doing then is putting a laptop between two hosts, bridging the connection and then sniffing traffic on that bridge (or one of its member interfaces)?

The only problem I have had with this is the bridge not learning MAC addresses quickly enough, or keeping addresses of the previous setup in the cache. It would probably be a good idea to cover some method of clearing the bridge cache when switching the location of the laptop.

The only advantage a tap would have over this setup would be a lower latency. For a tutorial though, the bridge setup may be a better idea, depending on the target audience. They are relatively easy to set up with XP.