Airtunes Question

I'd like to have a house-wide airtunes setup controllable from my iPhone (after 2.0) but I'm a little confused about how it works.

Specifically, I'd like to know if you can stream music from one iTunes computer to another and have the same music play on both computers. In other words, use one of the computers as an Airport Express?

Ideally, I'd like to have my music stream from one iTunes library to my speakers hooked up to an Apple TV, a different set of speakers hooked up to second computer, and yet a different set of speakers hooked up to a third computer- all streaming from one iTunes library (which is also playing the music on its own speakers).

I understand that Airport Express streams music, but what's the point of buying a few when I already have two laptops and an Airport Extreme in my house?

If this isn't possible with iTunes only, are there any third-party software that accomplish this?

Thanks!

 

Ok. Well, I know that Apple TV Take 2 definitely works with Airtunes like an Airport Express, I just wish iTunes-enabled computers did too. I could have some serious parties without buying more than one Airport Express just by plugging in some laptops into some speakers throughout the house.

Buying more than one Express just to stream music seems a little ridiculous.