MY family will soon be replacing the aging living room PC (an HP Pavilion slimline with an Athlon X2 250 and nForce 430 graphics). They've brought up the potential route of buying an optiplex or similar such desktop from goodwill or a government auction, so it won't come with windows. If they were to just drop the hard drive from the existing system into a new one, would they need to buy a new windows license, or would they have a fully working system?