How to change registered owner`s name on Windown XP:
1. Run regedit
2. Find and go to below key:

HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\Current Version

3. Change your name and organization  in following subkeys:

– RegisteredOwner

– RegisteredOrganization

URL: http://www.astahost.com/info.php/Change-Registered-Owners-Win-Xp_t2311.html