Administrator is no longer Administrator

On a WinXP Pro box, I go to the www.windowsupdate.com site
to check for updates. I get a message about having to be
an Administrator. I never got this before using the same
account.

So I login directly as Administrator and go to
www.windowsupdate.com and get the same message.

I go to Control Panel -> User Accounts and get an error
saying "wrong number of arguments or invalid property
assignment" and then just a blank window.

I try going to User and Groups under Computer Management.
It has a red cross out icon on it and accessing it gives
a "library not registered" error.

Any clue.