Here's how it works:
Airport Extreme is the base for ZeekNet, our wirelesss network (named in honor of our cat Zeek). It's hooked up to our cable modem which uses the same Comcast cable that also goes to our TV (as shown by the fatter wires in the diagram).
Sharing Music through iTunes
We have two computers on our wireless network, an iMac in the Office and a Mac Mini connected to the TV in the Living Room. The iMac is our main computer and is home to all of our music files, some of which also get synced to my iPhone and Ryan's Nano. Thanks to the Shared Music feature in iTunes, which lets you browse and play music from other computers running iTunes on your network, we can play all of our music from the Office in the Living Room on the Mac Mini. We use this method to play music through the TV and its attached speakers whenever we have guests. Using Shared Music, we can play all of our music from the Mac Mini in the Living Room or the iMac in the Office even though the files only exist in one location.
Wireless Speakers via Airport Express
The newest additions to the network are two sets of networked speakers--in the Basement, and as of yesterday, the Back Yard. These wireless speakers work simply by setting up an Airport Express and plugging speakers in. After configuring the airports to connect to the same network and giving each of them a name ("Basement" and "Back Yard") they automatically are recognized by iTunes through a feature called Air Tunes. This adds a drop down menu to the bottom corner if iTunes. The list includes checkboxes for "Computer" as in the one you're looking at iTunes on, and any configured AirPort Expresses ("Basement" and "Back Yard"). Check off where you want music and Voila! -- Music pumps throughout the house -- to the Basement and out into the Back Yard to add instant entertainment for those back yard bbqs.
Wireless Control via iPhone Remote
Even more amazing and magical is Apple's Remote application for iPhone (available from the App Store). When you're connected to your home wireless network and launch the Remote application, it figures out that iTunes is playing on one of your computers and instantly shows you the album cover and controls to adjust the volume, skip to the next song or even change to a different song or playlist. This feels magical because it's making all of this happen on your computer--from wherever you are in or around your house. Let's say you're playing bocce in the back yard and someone starts talking about the latest Killers song. Whip out the remote, tap a couple menus and instantly you've changed what's playing to that new Killers song. Oohs and Aaahs abound. Remote even lets you pick which wireless speakers the computer is playing music through. Move from Bocce in the Back Yard to Ping Pong in the basement? Turn off the music outside and turn it on downstairs without going anywhere near the computer. I love it.