To make this hint work, you need to have a FireWire drive with two ports on it, two FireWire cables, and two Macs with built-in FireWire. To make things easier, I turned off AirPort and disconnected the Ethernet -- I wanted to make sure that I was getting the full speed of the FireWire, as my second Mac only has 100base Ethernet capabilities.
Connect the FireWire drive to a Mac with file sharing set up on it, and then connect that drive's other FireWire port to any other Mac. Next enable networking over FireWire in the Networking System Preferences panel. In the setup panel, give the computers manual IP addresses -- I used 10.0.0.2 and 10.0.0.3, and a subnet mask of 255.255.255.0. Finally, simply connect to the Mac with the drive showing up in the Finder, and it will show up in sharing!
This allows you to network over FireWire and share a hard drive, which for me is useful for today's task of backing up all of my DVDs onto the drive. It could be useful for a multitude of tasks -- especially for older computers with FireWire and slower Ethernet.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080717051811427