Though Windows XP SP3 reached RTM status more than a week ago and subsequently trickled down to several download sites, it wasn't until today that the third service pack for Windows XP has been officially released to Windows Update for public consumption.
Currently, the final build is only available through Windows Update but the 300MB+ standalone installer is expected to become available throughout the day on the Microsoft Download Center. So, if you are still running the older but stable and mature XP version of Microsoft Windows go ahead and grab the update, which includes more than 1,100 hotfixes and patches as well as new features such as Network Access Protection and Black Hole Router detection.