Hello,
I'm trying to upgrade my PC. Can I install my old hard disc with its XP system and softwares within a new case (with its hardware)? Can I replace a hard disc by my old one, transplanting it from a pentium 3 to and AMD Athlon XP?
You can get lucky and it will work fine; however, sooner or later you might run in to problems due to driver conflicts caused by the unused drivers from your old hardware.