I recently completed a new whole house streaming music and audio system and I couldn't be happier. The best part....it wasn't that expensive. Let me show you how I did it.
Here is what you will need (some of this stuff you probably already have):
Apple TV
($99) - 1 for each room
Iphone or
Ipod Touch
- ($299)
Good wireless router 
- ($50 and up)
Networked PC or Mac with the ability to run Itunes
Speakers - Powered or Passive with AV Receiver
Television Set
The key to this whole solution is the Apple TV which allows you to stream audio and video from your PC to your TV/Speakers and control everything with an iphone or an ipod touch. Apple TV is inexpensive at $99 and very small, about the size of a hockey puck. You will need 1 in every room that you want to stream audio and/or video. With an ipod touch, you can control what songs or videos are playing in each room as well as the volume. You can even stream Pandora directly from your phone to one of your apple tv's.
Here is my living room setup.
1
Apple Mac Mini MC270LL/A Desktop
acting as a server for all of my audio and video with Itunes running.
1
Pioneer VSX-820-K 5.1 Home Theater Receiver
2
Infinity Primus Two-way 6 1/2-Inch Bookshelf/Satellite Speaker (Black, Each)
1 Samsung LCD TV
I hooked my Apple TV into my receiver using and HDMI cable, then ran an HDMI directly to my LCD TV. Then, I fired up my Apple TV and connected to my local network. You will want to make sure that homesharing is set-up in itunes on your computer. On Apple TV, choose computers then turn on Home Sharing. Enter your apple ID and password. After that, Apple TV will automatically find your itunes library.
Guess what? Thats all there is to it. You now have access to all of the music, videos, and photos that are in your itunes library. There are multiple ways to control your system, but my favorite way is to use the remote app (free) on your iphone or ipod touch. Fire up the app and it will automatically discover your Apple TV. You can use a touchpad remote to navigate directly on your tv, or, you can click done, and navigate your itunes library right on your screen, which is my favorite approach. Just select a song or video and it will almost immediately begin playing on Apple TV. If you just want music, you don't even need to turn your TV on. To play pandora, just fire up the Pandora App and click the icon in the lower right of your screen to start sending the music immediately to your apple TV. Another great option is Netflix. If you are a netflix subscriber you can access the entire Netflix streaming library from your Apple TV.
Very cool, very easy. Add as many Apple TV's as you need and control them all from your iphone or ipod touch. Apple TV has a lot of other great features as well that we'll explore on future posts. Enjoy.