Network MIDI is built into OS X 10.4, so if all your G5s are running Panther you're all set. I use MIDI Over LAN (www.musiclab.com) because it's cross-platform.
Also, I haven't figured out a way to get Network MIDI to address more than 16 channels per machine, but that may just be something I don't quite get.
Also, I haven't figured out a way to get Network MIDI to address more than 16 channels per machine, but that may just be something I don't quite get.