Have a burning desire to play your iTunes library from within the "10-foot interface" of Windows Media Center? Take a look at MCE Tunes, a third-party plug-in for WMCE computers that works with songs purchased from the iTunes store. MCE Tunes doesn’t decrypt the .m4a and .m4p files; instead, it simply enables those tunes to be played through WMCE, provided your PC is authorized to play the files in the first place. Since this is a Media Center plug-in, you can sit your bottom in front of your TV and navigate with a Media Center remote. A free trial works with unprotected tune-age to show you the interface; for playback of protected files, you’ll have to drop $30. I grabbed the free trial and saw all of my ripped music pulled in right away; there are synch settings to automatically update your WMCE library with iTunes as needed.
As a "streamer" who pipes digital and HD video content from my WMCE box to the Xbox 360, I was hoping for the ability to stream my iTunes library, but no support yet. However, the MCE Tunes folks are working on it and indicate a "free update to an extender-enabled version automatically" for registered users of the app.