I have bought Windows 7 pro edition which is downgradable. The question is how to downgrade ? After the downgrade what is going to be the s/n of the XP is it going to be the same S/N of the Windows 7 pro that I have downgraded ? And is it possible to install Windows XP with the Windows 7 pro serial number ? And if I want to end up with XP downgrade is it the only way ?