How to serve your iTunes library to your Sony PSP using WiFi internet is a nice little how-to for OS X users:
Dot Tunes looks at your iTunes library and generates a simple web page based on Album or Artist listings that can be accessed across the internet. Once you have generated the web page, it’s a simple matter of bookmarking the page in Safari and syncing that bookmark to your web browser on your PSP. You can then access your itunes library with the Dot Tunes web interface and easily navigate to a specific song by artist or album listing.
This isn’t actually PSP specific, as you could set this up as a way to serve up your music on your home system with a 200GB hard drive to serve the music out to your Powerbook while you are on the go.