I got FireWire working under System 7. My Solectron 1394 PCILynx card works but my Sonnet Allegro FW400 does not. If anybody has other FireWire cards and a PCI Mac that can run 7.5.5 or 7.6.1 to try it in, that'd be much appreciated... right now my table looks pretty sad with only two entries.
http://main.system7today.com/articles/firewire.html
http://main.system7today.com/articles/firewire.html