YES. Even a Mac to a PC. However it requires setup. And no $1 FW cables.
PC: Firewire ie1394 device - check if enabled and functioning in device manager.
Services - same need to be running as with ethernet.
Network Places: ie1394 device - right click, can test it, check status, or set it up in Properties.
Setup- TCP/IP - have to declare an IP for the FW on one computer. Or both.
Simple to do: use same numbers as ethernet conn., except edit last digit of I.P.
Create Network Connection - To the PC just created IP on is easiest.
HINT - Easier if no ethernet connection while setting it up.
MAC: Can check hardware status in system profiler/ firewire
Setup in Network: Show: Built in Firewire - create location and IP address on one,
other Mac can use DHCP or Automatic location. Check status - must have green to
proceed.
Sharing - enable at minimum Personal File Sharing
PC to MAC: even more to set on Mac.
My setup is Apple iMac G3-2001 to a Dell Dimension with standard FW card. Very handy because the Mac has only 2 USB ports, and they are USB 1.1 ultra slow version.
Once connected it is possible to share ethernet connection via FW - more to setup.