I'm not certain it's been suggested, and I may sound like a complete fool for suggesting this, but why not try damaging the zip extractor's code in order to make it ignore the password protection? Or, if it's something that invokes an access-denial function (what the hell would you call that?) inside the computer, edit part of the computer so that passwords no longer activate the denial function? I'm getting inspired by something I saw my friend do--he bypassed admin privileges by screwing around with the files needed to define what was password/admin protected and what wasn't.
I sincerely hope that this suggestions is actually of some help, and not ineffably stupid.