I've lost a Firewire DVD drive after the 10.6.4 update. I ran into this before after updating to Snow Leopard 10.6 from Leopard 10.5.
I installed this
fix which basically is just running the 10.5.8 IOFirewireSerialBusProtocolTransport.kext in place of the 10.6.x one. It worked at that time, but I tried it again after the 10.6.4 update and it didn't work this time.
Anyone get that Firewire fix to work?