I am the authority on this problem (since I have been having it since the PowerBook G4).
Basically here's the rundown.
Fact: a Canon GL2 (or, I assume, any other Canon DV camera) cannot share a FireWire bus with a FW hard drive. Period.
Fact: both the Firewire 800 and Firewire 400 ports on the MacBook Pro share the same FireWire bus. Therefore the Canon GL2 cannot coexist with a FireWire hard drive. (F***ING DOH!!! Can we say "MAJOR BUG"??)
Fact: this did NOT happen under OS 9, EVER.
Workaround A: buy yourself a FireWire 800 ExpressCard and connect your hard drive to that.
Workaround B: buy yourself a FireWire 400 ExpressCard and connect your camera to that.
(Both workarounds A and B work because they create a second FireWire bus thus ameliorating the problem.)
Workaround C: if your hard drive also has a USB interface, then connect it via USB (just make sure to use the right-hand side USB port, since the left-hand side one is notorious for being noisy and thus dropping frames during capture... just google "left hand USB port MacBook Pro" for a good laugh... thanks, Apple).
Workaround D: if your hard drive also has an eSATA port, buy yourself an eSATA ExpressCard and use that. Incidentally, AFAIK, this is the fastest drive interface, and is much better than FireWire 800. Pretty sure.
<rant> Incidentally, they SELL eSATA ExpressCards at the Apple store! LOL! They charge you $2500 for the computer, then you have to come back and they rape you for a card to make it work right! Apple should f****ing GIVE free eSATA cards to anyone who bought MacBook Pros and are having this problem... because I mean seriously, it should COME WITH an eSATA port built-in, to begin with, not to mention that FireWire is an interface that Apple freaking invented and so it should work with the Canon video cameras THAT APPLE ALSO SELLS. </rant>
-=DG=-