No sensible detail in your question. Which PC is the XP one, and what OS is the other? When you 'hooked it up' what do you mean? USB attached drive, drive direct to motherboard or what? If you have directly connected the old HDD to your m/b, have you disconnected your own HDD, or not? I dont yet understand why it would boot to the login screen - you dont want that to happen, and when it doesnt you will be fine.