I tend to always format my drives, but I don't zero them, in this particular installation, which might have been 10.3 or 10.4, I had cleanly installed OS X then OS 9 (the way my tibook's installs were handled) and within a few months the failure had happened.

It's only happened to me once, but I'm much more wary now, about OS X and 9 coexisting, except possibly in situations where one is required for the existance of the other, as in the case of my old powerbook G4, whose OS 9 installer was an OS X application.
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