Microsoft Corp. will change how users activate Windows XP when Service Pack 3 launches in the first half of 2008, a company white paper said. New installations of Windows XP SP3 will give users the same 30-day grace period currently offered to Windows Vista customers before they're required to enter a product activation key, the 25-character code that proves the copy is legitimate. "As in Windows Server 2003 SP2 and Windows Vista, users can now complete operating system installation without providing a product key during a full, integrated installation of Windows XP SP3," the Microsoft paper stated. "The operating system will prompt the user for a product key later as part of Genuine Advantage." With earlier editions of Windows XP, users must enter the activation key during the installation process itself; failing to do so, or using an invalid key, would result in the installation being blocked. The white paper, however, noted that the change does not apply to existing Windows XP installations upgraded to SP3. Those copies, which have presumably passed the activation stage previously, will not request the key again, Microsoft said.