Same issue here. I've got a ZR40, a very lightly used Apple-brand firewire cable, a year old macbook, leopard and iLife '08. No dice. This camera and cable worked well for me on a G4 tower, running panther, and iMovie 2/3.
I'll be quite surprised and disappointed if newer hardware and software has broken compatibility with a standard firewire DV camera. I'm on hold with apple phone support now; I'll update the message with what they tell me.