I've not had any luck sharing itunes files through the ps3 because of their protected format. If you rip your music into more "normal" formats (like mp3, for example), Tversity can stream that stuff to the PS3. You can also use the sharing in Windows Media Player similarly.
Here's a story on someone trying just that:
http://www.calvertgames.com/cgblog/2008/01/28/ps3-streaming-itunes-aac-files/Here's a forum thread on how to use Tversity with a PS3:
http://www.psu.com/forums/showthread.php?t=75081