USB 2.0 Slow on PowerBook G4 / Shooting tethered with D300

I recently resurrected my G4 Aluminum (replaced battery, Apple re-imaged to 10.5.5 in-store; 1.33 GHz 2 GB RAM).

I would like to use the laptop to shoot tethered with my Nikon D300. I am using a free app named Sofortbild to facilitate this.

When I take a picture on the camera (connected to the G4 via USB) it takes a REALLY long time to transfer the file. Like 30-60 seconds. Clearly not useful for real time shooting.

I did check the profiler to make sure I'm using 2.0. Also, I watched the transfer in Activity Monitor and it seemed to have a very sporadic transfer "pattern", where nothing would be written for a few seconds, then a lot would go across, etc. I don't believe it's the cabling, because I tried it on a PC and the transfer speeds were closer to a couple of seconds.

I set it all up again on my new generation iMac, and the speeds were also acceptable. Even though both are using USB 2.0, the iMac clearly outperforms the G4. However, I'm not sure why the G4 is working so slowly.

Is this just the way things are or are there other things I can do to imprive the transfer rate?

Thanks!

Been answered use Firewire USB ,even USB 2 is too slow, particularly on Macs.