I don't know any easy ways to stream to the X-Box, but, there are Several items on the market now that let you set up a media server on your PC and stream music to network players.
I personally use the Netgear MP101. It's not perfect, and is a pain to set up if you use WEP, but, It suits my needs just fine. It conects to your network via a standard 10bT style cable or through a wireless network (11.b or 11.g) It has output RCA jacks to attach to your stereo and a remote control to browse and play your music.
The server software is installed on your networked PC and catalogs all your MP3 and WMA files (does not support any other formats) You can then create playlists or just browse music by Genre, Artist, Track Name, Album Name.
Linksys and Creative Labs also make their own version of this. I'm not sure of the features or how they compare to the NetGear I use.
I'd like to stress, it's far from perfect and has its quirks, but, once it's set up properly it works very well. It's biggest virtue is that it's cheap. Around $100. Here's a link from newegg
http://www.newegg.com/app/view...T=DVD+Players+consumer
I've had one for about 6 months and use it daily. Last year I took a lot of time to rip my 20 year CD collection (500+ CDs) to MP3 format, and I really LOVE being able to access them all through this device.
