I just solved this problem for myself last night!
You must be running Windows Vista Home Premium, Enterprise, or Ultimate with all updates as of 5/25/07 installed. You just need to have Windows Media Player 11 installed (most of the time this is automatically done). When you navigate to Music on the Xross Media Bar (XMB), your PS3 should scan your network automatically devices on the network.
Make sure your User->Music->iTunes->iTunes Music folder is shared with at least all user read accesss w/ no password protection. If your PC name doesn't appear with a white WMP11 square next to it, you should be able to browse for your PC over the network. Once you have your PC selected, navigate through Music-> and all playable songs will be ready to play however you want to organize them!
NOTE: Supported formats for PS3 right now are .mp3, .wmv, and ATRAC-3, so if you (like me) need to convert your ENTIRE library from .aac to .mp3, it could take a while . . .
2ND NOTE: You can access your PC's music library through your PS3 then through your PSP through RemotePlay! Enjoy listening to your music anywhere you can get wireless internet access anywhere in the world! Any questions or comments feel free to email me sesshoumaru4b@gmail.com
Modified HP Pavillion 1560 Windows Vista