Recently, I had to change my Windows XP CD-key but couldn’t find where to start from. Just stumbled across a great article and am about do do a similar post.
Use the Activation Wizard
Warning: Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall your operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.