I'm guessing this is during an XP installation and that it gives that error and locks up during the 'copying os files' portion of the installation. That indicates a faulty CDROM or HDD. Try to reseat the IDE cables on both, and when I say reseat I don't mean just push in the IDE cables to see if they are all the way in. I mean unplug them and plug them back in. See if that does it. Could also be a problem CD. Oh, and an I/O error is Input/Output error.
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