Major Help

I have a really really really old laptop thats just laying around and i want to get it running an os just for testing, it has xp on it 10gb hard drive and 256 mb of ram i just want to use it to run scripts on it so i dont reck my other computers that make this one look like junk! My problem is i cant boot from usb and ive tried to run an install from a partitioned drive but i can back track or downgrade my os becuse it says…. cannot intsall becuase your os is newer than the install can someone help me?