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I picked up these on eBay for a fiver a go! They are tiny little Linux boxes that stream audio from a nominated PC on your network. The original Rio/Dell software is very 2002 and although adequate offers no integration with iTunes or Windows Media Player. When you power the box it shouts out a BootP request (that's an old protocol I haven't had to deal with since Phillips/Thompson routers of the mid-90s!) and that starts the download process of a tarball that has the Linux kernel to run the box. Once that's loaded it grabs an IP address via DHCP (from the same client software that serviced the BootP request - I guess not many people had home-routers when this was a product!) and you can then stream your MP3s to it. It has a nice display, IR remote and the audio output quality is good.
However, since it's demise it's become a target for home-brewers and hackers and there is a new kernel that makes it look like a Squeeze Player - the standard that Logitech have used for all of their home entertainment products. This makes it quite an interesting gadget as a network music/streamed radio player and it didn't take me very long to get it working with my Windows 7 media center. Using Logitech's server mean it integrates brilliantly with iTunes and you get access to all the BBC's iPlayer and streamed radio.
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Once you've got Squeezebox running you can use it to stream to WinAmp, your iPhone or even another instance of iTunes (rather perversely!).
So, here are the bits you need;
Rio's v. 1.04beta which was the last release. It's the only one that works with Windows 7 and it doesn't have all the instabilities previous releases had with 10 vs 100BaseT ethernet (this was the early noughties after all!).
SlimRIO is the tar-ball with the new kernel to make the box behave like a Logitech Squeeze player.
Squeezebox is the server that makes it all work nicely.
Finally you'll probably need a copy of the LAME encoder so that the server can transcode AAC, RealMedia etc into MP3 streams for live radio -
lame.exe - it needs to go in;
\Program Files\Squeezebox\server\bin