1. a computer running iTunes
2. a wifi network
3. an Air Tunes/airplay enabled device in each room you'll be streaming to.
4. (optional, but nice) an iPhone, ipad or iPod touch running the free "Remote" app to control the whole system.
The setup is basically a more affordable version of the excellent Sonos wireless music systems. If you already live in the iTunes/Apple ecosystem it can be even more affordable because you likely have some of the required components.
The airtunes/airplay devices listed above can be several things:
1. 99 dollar Apple Airport Express with a stereo mini-jack (connect via appropriate cable to powered speakers or a receiver)
2. 99 dollar Apple TV (streams video and audio but limited to optical or HDMI output)
3. Any of the coming AirPlay enabled powered speakers or receivers (iHome, Denon, etc)
Finally packed away 1980's stereo system. Miss the power of 50 watt speakers! Want to use Macpro to stream music/play iTunes library, with some sort of speaker system bigger than the usual desktop speakers. I listen to classical/jazz mostly and like to hear full range of the music. Intrigued by wireless systems for the portablity. I don't know much about Airtunes device, and wonder what possibilities that offers as for as speaker set-up.