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you can do it on any computer that has leopard.

No, you can't actually. :)

Late model Macbooks can run the Pwnage Tool ok, it's getting iTunes to recognize the phone in DFU mode that's the issue.
 
According to this thread you can either use a usb hub or replace the usb drivers in the latest build of leopard that comes on the new MB with the previous generation's drivers.
 
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