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A Simple Answer.

You said "video." Go with PowerBook with G4. Enough said.

If you want me to elaborate...

iBook G3 is merely adequate to get video work done. It will get the job done, but barely. PowerBook G4 will get the job done efficiently, meaning it will provide time and room for creativity, instead of wasting time drumming your fingers or tapping your foot on the floor while iBook renders transitions and effects and etc. Performance difference IS noticeable.

Here is a link for you to check out. Notice the comparisons regarding iMovie performance.
http://macspeedzone.com/html/hardware/machine/comparison/portable/powerbook/index.shtml

Also PowerBook now has SuperDrive. Trust me on this. Once you make a DVD, you'll never go back to making another tape. Ever.
 
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