Not sure if you mentioned if you were jailbroken but xbmc from cydia might help with that...it's free. Not sure if the app store version can though.
Are you referring to iTunes Network Share (DAAP)? which has its very own library sharing protocol, DAAP. XBMC can play all unprotected files, (ie. all files not purchased on iTunes Music Store, which can not be played in XBMC because they are encrypted with Apple's proprietary Digital Rights Management Scheme). To enable sharing in iTunes look under the edit tab, click on preferences, click on sharing and enable the sharing check box. To enable itunes sharing in XBMC edit the path of the source with the IP address of the PC you wish to connect to. It allows you to play audio files stored in your PC or MAC iTunes library. DAAP does have some limitations, including crossfading due to protocol structure.