Today I reinstalled XP on a machine and had to activate the Windows license prior to installing updates. At this URL (http://www.windowsitpro.com/article/john-savills-windows-faqs/how-do-i-activate-windows-xp-from-the-command-line-.aspx) I found a quick one-liner to start up the product activation GUI. Click Start, click Run and type “oobe/msoobe /a”. Be prepared to type in the 25-character activation string.