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For now, UUkeys Windows Password Recovery is the best program to reset XP login password. I followed the tutorial and it recovered my password in just 5 minutes: http://www.uukeys.com/reset-windows-xp-password.html
If you prefer an easy way to reset windows password, then you should use Windows Password Recovery instead. The steps are very simple and there are detailed instructions for each step.Tutorial: how to unlock windows password with uukeys
I don't know where to put the code. As a beginner, I prefer an easy solution like UUkeys Product Key Finder. You only need to take 2 clicks to get back the key.Tutorial: How to Find Lost Windows 7 Product Key