I'm surprised a bad RAM chip corrupted your XP installation. I've seen bad chips cause XP errors, but usually replacing the chip solves the problem.
If XP won't boot, even in safe mode, your safest option is to remove the hard drive and install it as a secondary drive in another Windows XP/2000 machine. If you only have access to one computer, I would purchase a new hard drive ($100), install it in your computer, and install Windows XP. You can then install the old hard drive in your machine as a secondary hard drive. Windows should recognize the drive and you should be able to retrieve the data.
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