Microsoft Windows XP Pro Performance Edition SP3 | 358 MbThis is a FULL Install. You CANNOT Upgrade from previous versions of Windows. There is no validation required. This PASSES WGA. This works 100 with Windows Update. I have included the CD-Key already in the install process. This means at no point will you have to enter it. Some people using Macs or Virtual Machines might need the serial. See Serial.txt if you do need it. Serial.txt is located in the download folder and in a folder on the disc/iso.