You can try Linux on it (or ask around if anyone wants to try Linux). It's a LOT easier to try Linux as a full install on a separate PC than it is to try a "live distro", as that way you can get online with your regular Windows/Mac PC and look for help when you can't get the Linux one to work right.
And most older hardware has Linux-compatible drivers, so problems are minimized.
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Nobody will pay for such a PC anymore.
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If you just want to toss it (or can't find it a new home) then find a wiping program and run that on it first, to get rid of the data on the hard drive (as well as easily possible). "Eraser" is the name of one that includes a feature to make a "Nuke Disk" that you boot off of to wipe a PC's hard drive.
Eraser is just a nice wiping program to have anyway--but the Nuke Disk is available alone from other places as well.
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