Though it's a solution we've mentioned before in the course of troubleshooting various USB and FireWire device issues, it is oft-overlooked and bears repeating: bad cables can be to blame for ...
Apple Computer has almost single-handedly succeeded in turning USB into an accepted interface standard. Sony, Apple, and others are currently making FireWire into the industry standard for multimedia.
Some (all?) DV camcorders transfer the raw DV data over Firewire but recompress the video when tranferring over USB. DV camcorders are really meant to be used with Firewire.