Originally Posted by brandoncross
You also need a dedicated firewire bus. Aren't all the firewire busses on macs connected? I know on a macpro you need a firewire card to run drives and other firewire stuff while the Mojo is connected to the internal firewire bus. I'm not really sure the imac's firewire bus can handle a mojo. If I where you, I'd try running a USB drive while using the Mojo on the internal firewire bus.
QuickTime DV works fine from memory, as for the separate bus issue, yes ideally you'd have it on a second bus, but the data rate is so low, it's fine on the same bus, exactly the same as the Canopus ADVC-100/110 was. A Mojo isn't a resource hungry HD device.
Check the system profiler to see if it is being detected on the Firewire bus. If not, restart with the Mojo turned off and then turn it on once the OS has loaded.