Umm.. you say that 100base-T is too slow for the B&W <-> PowerBook link, but then you mention AirPort, which is 1/10th of the speed.
Anyway, besides that, you can easily install multiple NICs in a machine running Mac OS X and maintain different networks/subnets on each one.
It's also possible to do in Mac OS 9, but it's much harder and requires additional software.
There is some discussion as to whether FireWire networking is viable or not. It wasn't last time i tried it, but others seem to think it is now, meaning you can connect the array to both machines via FireWire and each machine can access all drives at full FireWire speed.
Anyway, besides that, you can easily install multiple NICs in a machine running Mac OS X and maintain different networks/subnets on each one.
It's also possible to do in Mac OS 9, but it's much harder and requires additional software.
There is some discussion as to whether FireWire networking is viable or not. It wasn't last time i tried it, but others seem to think it is now, meaning you can connect the array to both machines via FireWire and each machine can access all drives at full FireWire speed.