Keep two iTunes Libraries and Media in sync

I'm retiring my powerbook to act as a sort of media server, replacing it with a macbook pro. i want to use my powerbook to stream media to my xbox, airport, etc, but want to have all of my music on my macbook pro. Therefore, I need to find a way to (hopefully automatically- maybe with an apple script?) keep my iTunes library and media files in sync. I realize that I can stream from my macbook pro, however it is not always on and/or connected to my network. How can I keep my iTunes library (music only) synced between both computers.

To reiterate, the files need to be located on BOTH computers.

Thanks in advance.

I think Home Sharing would work for your iTunes libraries. iTunes 9: Understanding Home Sharing