Ok, I successfully installed DBI on my MacMini and 15 inch PowerBook G4, so the problem is with some configuration on my PowerMac G4 MDD( the computer I'm having problems installing DBI on ). When CPAN asked me for the 'working' directory the first time I set it up on my PowerMac G4, I changed it to my desktop. I think this might be the problem.
It might be the cause of the problem, though I doubt it. You can rerun the whole configuration process with the command o conf init at the CPAN prompt, and choose the default working directory (which should be ~/.cpan).
(Oh and by the way, you can simply edit one of your message by clicking the link pointing to it)