Any of the OHCI (Open Host Controller Interface) compliant cards should work fine with your PowerBook. Make sure you have plenty of RAM (128-1256MB), and plenty of space available on your internal disk. I've used iMovie on a 292MHz WallStreet and it is very useable for smaller projects.
I'm not sure if CardBus offers enough bandwidth to control the camera, preview on the camera, and read/write data from an external firewire disk, but it may be your only option if you still have the original 2GB disk in your 'Book.
Good luck!
BTW - Don't expect stuff to render all that fast, and I doubt you will get the full screen prieview to work well.
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