I did have installed a XP Corporate SP2, up to date with current Windows Update, and wanted to change this into my Windows XP SP2 Professional, that I recently bought. Ok, what worked and what not worked: -changing the key with a keychanger did NOT work, the new key did not take, but that is because Corp has some files different (hence those early cracks for XP that changed pro to corp) - Updating from within XP did not work, as the legit refused to install on that system. - Marsden's way DID work. The repair stumbled over my keyboard-usb drivers and I had to connect it to PS2. Then I had to activate by phone, as it wouldn't let me log on but my firewall (Outpost) was already active and prevented XP from calling home. Now I only need to hack uxtheme.dll again, visit windows update and do some other cosmetics but I got a legit XP. Thanks for the help and I hope this might be helpful to others that will try this. IF anyone insists I could even compare the files and find out which ones were different.