It seems a bit strained that the update site check all Microsoft installations and then block update all over if a pirated copy is found. I don´t belive they are allowed to perform this kind of punishment because it affects legal copies as well. It´s more likely caused by the XP keys you used. Have you tried to use the Office update?
If the problem remain then use the updatesite for Corp Editions:_http://v4.windowsupdate.microsoft.com/en/default.asp?corporate=true
LaZorMan